Showing 57 of 75 total issues
Function has a complexity of 11. Open
bloombox.setup = function(partner, location, apikey, callback, extraConfig) {
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- Exclude checks
Limit Cyclomatic Complexity (complexity)
Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.
function a(x) {
if (true) {
return x; // 1st path
} else if (false) {
return x+1; // 2nd path
} else {
return 4; // 3rd path
}
}
Rule Details
This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20
).
Examples of incorrect code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else if (false) {
return x+1;
} else {
return 4; // 3rd path
}
}
Examples of correct code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else {
return 4;
}
}
Options
Optionally, you may specify a max
object property:
"complexity": ["error", 2]
is equivalent to
"complexity": ["error", { "max": 2 }]
Deprecated: the object property maximum
is deprecated. Please use the property max
instead.
When Not To Use It
If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.
Further Reading
Related Rules
- [max-depth](max-depth.md)
- [max-len](max-len.md)
- [max-nested-callbacks](max-nested-callbacks.md)
- [max-params](max-params.md)
- [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/
Function has a complexity of 8. Open
this.stream.on('data', function(responsePayload) {
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- Exclude checks
Limit Cyclomatic Complexity (complexity)
Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.
function a(x) {
if (true) {
return x; // 1st path
} else if (false) {
return x+1; // 2nd path
} else {
return 4; // 3rd path
}
}
Rule Details
This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20
).
Examples of incorrect code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else if (false) {
return x+1;
} else {
return 4; // 3rd path
}
}
Examples of correct code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else {
return 4;
}
}
Options
Optionally, you may specify a max
object property:
"complexity": ["error", 2]
is equivalent to
"complexity": ["error", { "max": 2 }]
Deprecated: the object property maximum
is deprecated. Please use the property max
instead.
When Not To Use It
If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.
Further Reading
Related Rules
- [max-depth](max-depth.md)
- [max-len](max-len.md)
- [max-nested-callbacks](max-nested-callbacks.md)
- [max-params](max-params.md)
- [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/
Function has a complexity of 8. Open
bloombox.util.generateUUID = function() {
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- Exclude checks
Limit Cyclomatic Complexity (complexity)
Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.
function a(x) {
if (true) {
return x; // 1st path
} else if (false) {
return x+1; // 2nd path
} else {
return 4; // 3rd path
}
}
Rule Details
This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20
).
Examples of incorrect code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else if (false) {
return x+1;
} else {
return 4; // 3rd path
}
}
Examples of correct code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else {
return 4;
}
}
Options
Optionally, you may specify a max
object property:
"complexity": ["error", 2]
is equivalent to
"complexity": ["error", { "max": 2 }]
Deprecated: the object property maximum
is deprecated. Please use the property max
instead.
When Not To Use It
If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.
Further Reading
Related Rules
- [max-depth](max-depth.md)
- [max-len](max-len.md)
- [max-nested-callbacks](max-nested-callbacks.md)
- [max-params](max-params.md)
- [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/
Static method 'fromObject' has a complexity of 8. Open
static fromObject(record) {
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- Exclude checks
Limit Cyclomatic Complexity (complexity)
Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.
function a(x) {
if (true) {
return x; // 1st path
} else if (false) {
return x+1; // 2nd path
} else {
return 4; // 3rd path
}
}
Rule Details
This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20
).
Examples of incorrect code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else if (false) {
return x+1;
} else {
return 4; // 3rd path
}
}
Examples of correct code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else {
return 4;
}
}
Options
Optionally, you may specify a max
object property:
"complexity": ["error", 2]
is equivalent to
"complexity": ["error", { "max": 2 }]
Deprecated: the object property maximum
is deprecated. Please use the property max
instead.
When Not To Use It
If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.
Further Reading
Related Rules
- [max-depth](max-depth.md)
- [max-len](max-len.md)
- [max-nested-callbacks](max-nested-callbacks.md)
- [max-params](max-params.md)
- [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/
Function 'prepRetrieveRequest' has a complexity of 8. Open
function prepRetrieveRequest(config) {
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- Exclude checks
Limit Cyclomatic Complexity (complexity)
Cyclomatic complexity measures the number of linearly independent paths through a program's source code. This rule allows setting a cyclomatic complexity threshold.
function a(x) {
if (true) {
return x; // 1st path
} else if (false) {
return x+1; // 2nd path
} else {
return 4; // 3rd path
}
}
Rule Details
This rule is aimed at reducing code complexity by capping the amount of cyclomatic complexity allowed in a program. As such, it will warn when the cyclomatic complexity crosses the configured threshold (default is 20
).
Examples of incorrect code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else if (false) {
return x+1;
} else {
return 4; // 3rd path
}
}
Examples of correct code for a maximum of 2:
/*eslint complexity: ["error", 2]*/
function a(x) {
if (true) {
return x;
} else {
return 4;
}
}
Options
Optionally, you may specify a max
object property:
"complexity": ["error", 2]
is equivalent to
"complexity": ["error", { "max": 2 }]
Deprecated: the object property maximum
is deprecated. Please use the property max
instead.
When Not To Use It
If you can't determine an appropriate complexity limit for your code, then it's best to disable this rule.
Further Reading
Related Rules
- [max-depth](max-depth.md)
- [max-len](max-len.md)
- [max-nested-callbacks](max-nested-callbacks.md)
- [max-params](max-params.md)
- [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/
Identical blocks of code found in 2 locations. Consider refactoring. Open
this.remote.product(key,
function(response, err) {
if (err) reject(err);
else if (response) resolve(response);
}, config);
- Read upRead up
Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 47.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Identical blocks of code found in 2 locations. Consider refactoring. Open
if (!db || config && config.fresh) this.remote.product(key,
function(response, err) {
if (err) reject(err);
else if (response) resolve(response);
}, config);
- Read upRead up
Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 47.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Expected an assignment or function call and instead saw an expression. Open
bloombox.menu.RetrieveConfig;
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- Exclude checks
Disallow Unused Expressions (no-unused-expressions)
An unused expression which has no effect on the state of the program indicates a logic error.
For example, n + 1;
is not a syntax error, but it might be a typing mistake where a programmer meant an assignment statement n += 1;
instead.
Rule Details
This rule aims to eliminate unused expressions which have no effect on the state of the program.
This rule does not apply to function calls or constructor calls with the new
operator, because they could have side effects on the state of the program.
var i = 0;
function increment() { i += 1; }
increment(); // return value is unused, but i changed as a side effect
var nThings = 0;
function Thing() { nThings += 1; }
new Thing(); // constructed object is unused, but nThings changed as a side effect
This rule does not apply to directives (which are in the form of literal string expressions such as "use strict";
at the beginning of a script, module, or function).
Sequence expressions (those using a comma, such as a = 1, b = 2
) are always considered unused unless their return value is assigned or used in a condition evaluation, or a function call is made with the sequence expression value.
Options
This rule, in its default state, does not require any arguments. If you would like to enable one or more of the following you may pass an object with the options set as follows:
-
allowShortCircuit
set totrue
will allow you to use short circuit evaluations in your expressions (Default:false
). -
allowTernary
set totrue
will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default:false
). -
allowTaggedTemplates
set totrue
will enable you to use tagged template literals in your expressions (Default:false
).
These options allow unused expressions only if all of the code paths either directly change the state (for example, assignment statement) or could have side effects (for example, function call).
Examples of incorrect code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
0
if(0) 0
{0}
f(0), {}
a && b()
a, b()
c = a, b;
a() && function namedFunctionInExpressionContext () {f();}
(function anIncompleteIIFE () {});
injectGlobal`body{ color: red; }`
Note that one or more string expression statements (with or without semi-colons) will only be considered as unused if they are not in the beginning of a script, module, or function (alone and uninterrupted by other statements). Otherwise, they will be treated as part of a "directive prologue", a section potentially usable by JavaScript engines. This includes "strict mode" directives.
"use strict";
"use asm"
"use stricter";
"use babel"
"any other strings like this in the prologue";
Examples of correct code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
{} // In this context, this is a block statement, not an object literal
{myLabel: someVar} // In this context, this is a block statement with a label and expression, not an object literal
function namedFunctionDeclaration () {}
(function aGenuineIIFE () {}());
f()
a = 0
new C
delete a.b
void a
allowShortCircuit
Examples of incorrect code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a || b
Examples of correct code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a && b()
a() || (b = c)
allowTernary
Examples of incorrect code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b : 0
a ? b : c()
Examples of correct code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b() : c()
a ? (b = c) : d()
allowShortCircuit and allowTernary
Examples of correct code for the { "allowShortCircuit": true, "allowTernary": true }
options:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true, "allowTernary": true }]*/
a ? b() || (c = d) : e()
allowTaggedTemplates
Examples of incorrect code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
`some untagged template string`;
Examples of correct code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
tag`some tagged template string`;
Source: http://eslint.org/docs/rules/
Use ‘===’ to compare with ‘null’. Open
if (bloombox.menu.lastSeenFingerprint != null) {
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- Exclude checks
Disallow Null Comparisons (no-eq-null)
Comparing to null
without a type-checking operator (==
or !=
), can have unintended results as the comparison will evaluate to true when comparing to not just a null
, but also an undefined
value.
if (foo == null) {
bar();
}
Rule Details
The no-eq-null
rule aims reduce potential bug and unwanted behavior by ensuring that comparisons to null
only match null
, and not also undefined
. As such it will flag comparisons to null when using ==
and !=
.
Examples of incorrect code for this rule:
/*eslint no-eq-null: "error"*/
if (foo == null) {
bar();
}
while (qux != null) {
baz();
}
Examples of correct code for this rule:
/*eslint no-eq-null: "error"*/
if (foo === null) {
bar();
}
while (qux !== null) {
baz();
}
Source: http://eslint.org/docs/rules/
Expected '!==' and instead saw '!='. Open
if (value != null && typeof value === 'object') {
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- Exclude checks
Require === and !== (eqeqeq)
It is considered good practice to use the type-safe equality operators ===
and !==
instead of their regular counterparts ==
and !=
.
The reason for this is that ==
and !=
do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm.
For instance, the following statements are all considered true
:
[] == false
[] == ![]
3 == "03"
If one of those occurs in an innocent-looking statement such as a == b
the actual problem is very difficult to spot.
Rule Details
This rule is aimed at eliminating the type-unsafe equality operators.
Examples of incorrect code for this rule:
/*eslint eqeqeq: "error"*/
if (x == 42) { }
if ("" == text) { }
if (obj.getStuff() != undefined) { }
The --fix
option on the command line automatically fixes some problems reported by this rule. A problem is only fixed if one of the operands is a typeof
expression, or if both operands are literals with the same type.
Options
always
The "always"
option (default) enforces the use of ===
and !==
in every situation (except when you opt-in to more specific handling of null
[see below]).
Examples of incorrect code for the "always"
option:
/*eslint eqeqeq: ["error", "always"]*/
a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null
Examples of correct code for the "always"
option:
/*eslint eqeqeq: ["error", "always"]*/
a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null
This rule optionally takes a second argument, which should be an object with the following supported properties:
-
"null"
: Customize how this rule treatsnull
literals. Possible values:-
always
(default) - Always use === or !==. -
never
- Never use === or !== withnull
. -
ignore
- Do not apply this rule tonull
.
-
smart
The "smart"
option enforces the use of ===
and !==
except for these cases:
- Comparing two literal values
- Evaluating the value of
typeof
- Comparing against
null
Examples of incorrect code for the "smart"
option:
/*eslint eqeqeq: ["error", "smart"]*/
// comparing two variables requires ===
a == b
// only one side is a literal
foo == true
bananas != 1
// comparing to undefined requires ===
value == undefined
Examples of correct code for the "smart"
option:
/*eslint eqeqeq: ["error", "smart"]*/
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null
allow-null
Deprecated: Instead of using this option use "always" and pass a "null" option property with value "ignore". This will tell eslint to always enforce strict equality except when comparing with the null
literal.
["error", "always", {"null": "ignore"}]
When Not To Use It
If you don't want to enforce a style for using equality operators, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/
Expected return with your callback function. Open
if (callback) callback(null, err);
- Read upRead up
- Exclude checks
Enforce Return After Callback (callback-return)
The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.
function doSomething(err, callback) {
if (err) {
return callback(err);
}
callback();
}
To prevent calling the callback multiple times it is important to return
anytime the callback is triggered outside
of the main function body. Neglecting this technique often leads to issues where you do something more than once.
For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw
a Can't render headers after they are sent to the client.
error.
Rule Details
This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately
preceding a return
statement. This rule decides what is a callback based on the name of the function being called.
Options
The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback
, cb
, next
.
Default callback names
Examples of incorrect code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err);
}
callback();
}
Examples of correct code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
return callback(err);
}
callback();
}
Supplied callback names
Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
done(err);
}
done();
}
function bar(err, send) {
if (err) {
send.error(err);
}
send.success();
}
Examples of correct code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
return done(err);
}
done();
}
function bar(err, send) {
if (err) {
return send.error(err);
}
send.success();
}
Known Limitations
Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:
- false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
- false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)
Passing the callback by reference
The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout
).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
setTimeout(callback, 0); // this is bad, but WILL NOT warn
}
callback();
}
Triggering the callback within a nested function
The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
process.nextTick(function() {
return callback(); // this is bad, but WILL NOT warn
});
}
callback();
}
If/else statements
The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if
statement.
Example of a false positive when this rule reports incorrect code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err); // this is fine, but WILL warn
} else {
callback(); // this is fine, but WILL warn
}
}
When Not To Use It
There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.
Further Reading
Related Rules
- [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/
Expected return with your callback function. Open
if (callback) callback(response, null);
- Read upRead up
- Exclude checks
Enforce Return After Callback (callback-return)
The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.
function doSomething(err, callback) {
if (err) {
return callback(err);
}
callback();
}
To prevent calling the callback multiple times it is important to return
anytime the callback is triggered outside
of the main function body. Neglecting this technique often leads to issues where you do something more than once.
For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw
a Can't render headers after they are sent to the client.
error.
Rule Details
This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately
preceding a return
statement. This rule decides what is a callback based on the name of the function being called.
Options
The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback
, cb
, next
.
Default callback names
Examples of incorrect code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err);
}
callback();
}
Examples of correct code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
return callback(err);
}
callback();
}
Supplied callback names
Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
done(err);
}
done();
}
function bar(err, send) {
if (err) {
send.error(err);
}
send.success();
}
Examples of correct code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
return done(err);
}
done();
}
function bar(err, send) {
if (err) {
return send.error(err);
}
send.success();
}
Known Limitations
Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:
- false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
- false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)
Passing the callback by reference
The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout
).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
setTimeout(callback, 0); // this is bad, but WILL NOT warn
}
callback();
}
Triggering the callback within a nested function
The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
process.nextTick(function() {
return callback(); // this is bad, but WILL NOT warn
});
}
callback();
}
If/else statements
The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if
statement.
Example of a false positive when this rule reports incorrect code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err); // this is fine, but WILL warn
} else {
callback(); // this is fine, but WILL warn
}
}
When Not To Use It
There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.
Further Reading
Related Rules
- [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/
Expected return with your callback function. Open
if (callback) callback(false, err);
- Read upRead up
- Exclude checks
Enforce Return After Callback (callback-return)
The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.
function doSomething(err, callback) {
if (err) {
return callback(err);
}
callback();
}
To prevent calling the callback multiple times it is important to return
anytime the callback is triggered outside
of the main function body. Neglecting this technique often leads to issues where you do something more than once.
For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw
a Can't render headers after they are sent to the client.
error.
Rule Details
This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately
preceding a return
statement. This rule decides what is a callback based on the name of the function being called.
Options
The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback
, cb
, next
.
Default callback names
Examples of incorrect code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err);
}
callback();
}
Examples of correct code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
return callback(err);
}
callback();
}
Supplied callback names
Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
done(err);
}
done();
}
function bar(err, send) {
if (err) {
send.error(err);
}
send.success();
}
Examples of correct code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
return done(err);
}
done();
}
function bar(err, send) {
if (err) {
return send.error(err);
}
send.success();
}
Known Limitations
Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:
- false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
- false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)
Passing the callback by reference
The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout
).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
setTimeout(callback, 0); // this is bad, but WILL NOT warn
}
callback();
}
Triggering the callback within a nested function
The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
process.nextTick(function() {
return callback(); // this is bad, but WILL NOT warn
});
}
callback();
}
If/else statements
The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if
statement.
Example of a false positive when this rule reports incorrect code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err); // this is fine, but WILL warn
} else {
callback(); // this is fine, but WILL warn
}
}
When Not To Use It
There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.
Further Reading
Related Rules
- [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/
Expected an assignment or function call and instead saw an expression. Open
bloombox.menu.ObservableMenuCancelCallback;
- Read upRead up
- Exclude checks
Disallow Unused Expressions (no-unused-expressions)
An unused expression which has no effect on the state of the program indicates a logic error.
For example, n + 1;
is not a syntax error, but it might be a typing mistake where a programmer meant an assignment statement n += 1;
instead.
Rule Details
This rule aims to eliminate unused expressions which have no effect on the state of the program.
This rule does not apply to function calls or constructor calls with the new
operator, because they could have side effects on the state of the program.
var i = 0;
function increment() { i += 1; }
increment(); // return value is unused, but i changed as a side effect
var nThings = 0;
function Thing() { nThings += 1; }
new Thing(); // constructed object is unused, but nThings changed as a side effect
This rule does not apply to directives (which are in the form of literal string expressions such as "use strict";
at the beginning of a script, module, or function).
Sequence expressions (those using a comma, such as a = 1, b = 2
) are always considered unused unless their return value is assigned or used in a condition evaluation, or a function call is made with the sequence expression value.
Options
This rule, in its default state, does not require any arguments. If you would like to enable one or more of the following you may pass an object with the options set as follows:
-
allowShortCircuit
set totrue
will allow you to use short circuit evaluations in your expressions (Default:false
). -
allowTernary
set totrue
will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default:false
). -
allowTaggedTemplates
set totrue
will enable you to use tagged template literals in your expressions (Default:false
).
These options allow unused expressions only if all of the code paths either directly change the state (for example, assignment statement) or could have side effects (for example, function call).
Examples of incorrect code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
0
if(0) 0
{0}
f(0), {}
a && b()
a, b()
c = a, b;
a() && function namedFunctionInExpressionContext () {f();}
(function anIncompleteIIFE () {});
injectGlobal`body{ color: red; }`
Note that one or more string expression statements (with or without semi-colons) will only be considered as unused if they are not in the beginning of a script, module, or function (alone and uninterrupted by other statements). Otherwise, they will be treated as part of a "directive prologue", a section potentially usable by JavaScript engines. This includes "strict mode" directives.
"use strict";
"use asm"
"use stricter";
"use babel"
"any other strings like this in the prologue";
Examples of correct code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
{} // In this context, this is a block statement, not an object literal
{myLabel: someVar} // In this context, this is a block statement with a label and expression, not an object literal
function namedFunctionDeclaration () {}
(function aGenuineIIFE () {}());
f()
a = 0
new C
delete a.b
void a
allowShortCircuit
Examples of incorrect code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a || b
Examples of correct code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a && b()
a() || (b = c)
allowTernary
Examples of incorrect code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b : 0
a ? b : c()
Examples of correct code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b() : c()
a ? (b = c) : d()
allowShortCircuit and allowTernary
Examples of correct code for the { "allowShortCircuit": true, "allowTernary": true }
options:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true, "allowTernary": true }]*/
a ? b() || (c = d) : e()
allowTaggedTemplates
Examples of incorrect code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
`some untagged template string`;
Examples of correct code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
tag`some tagged template string`;
Source: http://eslint.org/docs/rules/
Expected an assignment or function call and instead saw an expression. Open
bloombox.menu.ObservableMenuErrorCallback;
- Read upRead up
- Exclude checks
Disallow Unused Expressions (no-unused-expressions)
An unused expression which has no effect on the state of the program indicates a logic error.
For example, n + 1;
is not a syntax error, but it might be a typing mistake where a programmer meant an assignment statement n += 1;
instead.
Rule Details
This rule aims to eliminate unused expressions which have no effect on the state of the program.
This rule does not apply to function calls or constructor calls with the new
operator, because they could have side effects on the state of the program.
var i = 0;
function increment() { i += 1; }
increment(); // return value is unused, but i changed as a side effect
var nThings = 0;
function Thing() { nThings += 1; }
new Thing(); // constructed object is unused, but nThings changed as a side effect
This rule does not apply to directives (which are in the form of literal string expressions such as "use strict";
at the beginning of a script, module, or function).
Sequence expressions (those using a comma, such as a = 1, b = 2
) are always considered unused unless their return value is assigned or used in a condition evaluation, or a function call is made with the sequence expression value.
Options
This rule, in its default state, does not require any arguments. If you would like to enable one or more of the following you may pass an object with the options set as follows:
-
allowShortCircuit
set totrue
will allow you to use short circuit evaluations in your expressions (Default:false
). -
allowTernary
set totrue
will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default:false
). -
allowTaggedTemplates
set totrue
will enable you to use tagged template literals in your expressions (Default:false
).
These options allow unused expressions only if all of the code paths either directly change the state (for example, assignment statement) or could have side effects (for example, function call).
Examples of incorrect code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
0
if(0) 0
{0}
f(0), {}
a && b()
a, b()
c = a, b;
a() && function namedFunctionInExpressionContext () {f();}
(function anIncompleteIIFE () {});
injectGlobal`body{ color: red; }`
Note that one or more string expression statements (with or without semi-colons) will only be considered as unused if they are not in the beginning of a script, module, or function (alone and uninterrupted by other statements). Otherwise, they will be treated as part of a "directive prologue", a section potentially usable by JavaScript engines. This includes "strict mode" directives.
"use strict";
"use asm"
"use stricter";
"use babel"
"any other strings like this in the prologue";
Examples of correct code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
{} // In this context, this is a block statement, not an object literal
{myLabel: someVar} // In this context, this is a block statement with a label and expression, not an object literal
function namedFunctionDeclaration () {}
(function aGenuineIIFE () {}());
f()
a = 0
new C
delete a.b
void a
allowShortCircuit
Examples of incorrect code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a || b
Examples of correct code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a && b()
a() || (b = c)
allowTernary
Examples of incorrect code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b : 0
a ? b : c()
Examples of correct code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b() : c()
a ? (b = c) : d()
allowShortCircuit and allowTernary
Examples of correct code for the { "allowShortCircuit": true, "allowTernary": true }
options:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true, "allowTernary": true }]*/
a ? b() || (c = d) : e()
allowTaggedTemplates
Examples of incorrect code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
`some untagged template string`;
Examples of correct code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
tag`some tagged template string`;
Source: http://eslint.org/docs/rules/
Expected an assignment or function call and instead saw an expression. Open
bloombox.telemetry.PingCallback;
- Read upRead up
- Exclude checks
Disallow Unused Expressions (no-unused-expressions)
An unused expression which has no effect on the state of the program indicates a logic error.
For example, n + 1;
is not a syntax error, but it might be a typing mistake where a programmer meant an assignment statement n += 1;
instead.
Rule Details
This rule aims to eliminate unused expressions which have no effect on the state of the program.
This rule does not apply to function calls or constructor calls with the new
operator, because they could have side effects on the state of the program.
var i = 0;
function increment() { i += 1; }
increment(); // return value is unused, but i changed as a side effect
var nThings = 0;
function Thing() { nThings += 1; }
new Thing(); // constructed object is unused, but nThings changed as a side effect
This rule does not apply to directives (which are in the form of literal string expressions such as "use strict";
at the beginning of a script, module, or function).
Sequence expressions (those using a comma, such as a = 1, b = 2
) are always considered unused unless their return value is assigned or used in a condition evaluation, or a function call is made with the sequence expression value.
Options
This rule, in its default state, does not require any arguments. If you would like to enable one or more of the following you may pass an object with the options set as follows:
-
allowShortCircuit
set totrue
will allow you to use short circuit evaluations in your expressions (Default:false
). -
allowTernary
set totrue
will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default:false
). -
allowTaggedTemplates
set totrue
will enable you to use tagged template literals in your expressions (Default:false
).
These options allow unused expressions only if all of the code paths either directly change the state (for example, assignment statement) or could have side effects (for example, function call).
Examples of incorrect code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
0
if(0) 0
{0}
f(0), {}
a && b()
a, b()
c = a, b;
a() && function namedFunctionInExpressionContext () {f();}
(function anIncompleteIIFE () {});
injectGlobal`body{ color: red; }`
Note that one or more string expression statements (with or without semi-colons) will only be considered as unused if they are not in the beginning of a script, module, or function (alone and uninterrupted by other statements). Otherwise, they will be treated as part of a "directive prologue", a section potentially usable by JavaScript engines. This includes "strict mode" directives.
"use strict";
"use asm"
"use stricter";
"use babel"
"any other strings like this in the prologue";
Examples of correct code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
{} // In this context, this is a block statement, not an object literal
{myLabel: someVar} // In this context, this is a block statement with a label and expression, not an object literal
function namedFunctionDeclaration () {}
(function aGenuineIIFE () {}());
f()
a = 0
new C
delete a.b
void a
allowShortCircuit
Examples of incorrect code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a || b
Examples of correct code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a && b()
a() || (b = c)
allowTernary
Examples of incorrect code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b : 0
a ? b : c()
Examples of correct code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b() : c()
a ? (b = c) : d()
allowShortCircuit and allowTernary
Examples of correct code for the { "allowShortCircuit": true, "allowTernary": true }
options:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true, "allowTernary": true }]*/
a ? b() || (c = d) : e()
allowTaggedTemplates
Examples of incorrect code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
`some untagged template string`;
Examples of correct code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
tag`some tagged template string`;
Source: http://eslint.org/docs/rules/
Expected return with your callback function. Open
callback(response, null);
- Read upRead up
- Exclude checks
Enforce Return After Callback (callback-return)
The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.
function doSomething(err, callback) {
if (err) {
return callback(err);
}
callback();
}
To prevent calling the callback multiple times it is important to return
anytime the callback is triggered outside
of the main function body. Neglecting this technique often leads to issues where you do something more than once.
For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw
a Can't render headers after they are sent to the client.
error.
Rule Details
This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately
preceding a return
statement. This rule decides what is a callback based on the name of the function being called.
Options
The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback
, cb
, next
.
Default callback names
Examples of incorrect code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err);
}
callback();
}
Examples of correct code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
return callback(err);
}
callback();
}
Supplied callback names
Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
done(err);
}
done();
}
function bar(err, send) {
if (err) {
send.error(err);
}
send.success();
}
Examples of correct code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
return done(err);
}
done();
}
function bar(err, send) {
if (err) {
return send.error(err);
}
send.success();
}
Known Limitations
Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:
- false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
- false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)
Passing the callback by reference
The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout
).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
setTimeout(callback, 0); // this is bad, but WILL NOT warn
}
callback();
}
Triggering the callback within a nested function
The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
process.nextTick(function() {
return callback(); // this is bad, but WILL NOT warn
});
}
callback();
}
If/else statements
The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if
statement.
Example of a false positive when this rule reports incorrect code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err); // this is fine, but WILL warn
} else {
callback(); // this is fine, but WILL warn
}
}
When Not To Use It
There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.
Further Reading
Related Rules
- [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/
Expected return with your callback function. Open
callback(resp, null);
- Read upRead up
- Exclude checks
Enforce Return After Callback (callback-return)
The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.
function doSomething(err, callback) {
if (err) {
return callback(err);
}
callback();
}
To prevent calling the callback multiple times it is important to return
anytime the callback is triggered outside
of the main function body. Neglecting this technique often leads to issues where you do something more than once.
For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw
a Can't render headers after they are sent to the client.
error.
Rule Details
This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately
preceding a return
statement. This rule decides what is a callback based on the name of the function being called.
Options
The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback
, cb
, next
.
Default callback names
Examples of incorrect code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err);
}
callback();
}
Examples of correct code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
return callback(err);
}
callback();
}
Supplied callback names
Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
done(err);
}
done();
}
function bar(err, send) {
if (err) {
send.error(err);
}
send.success();
}
Examples of correct code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
return done(err);
}
done();
}
function bar(err, send) {
if (err) {
return send.error(err);
}
send.success();
}
Known Limitations
Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:
- false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
- false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)
Passing the callback by reference
The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout
).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
setTimeout(callback, 0); // this is bad, but WILL NOT warn
}
callback();
}
Triggering the callback within a nested function
The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
process.nextTick(function() {
return callback(); // this is bad, but WILL NOT warn
});
}
callback();
}
If/else statements
The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if
statement.
Example of a false positive when this rule reports incorrect code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err); // this is fine, but WILL warn
} else {
callback(); // this is fine, but WILL warn
}
}
When Not To Use It
There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.
Further Reading
Related Rules
- [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/
Expected an assignment or function call and instead saw an expression. Open
bloombox.menu.ObservableMenuReactor;
- Read upRead up
- Exclude checks
Disallow Unused Expressions (no-unused-expressions)
An unused expression which has no effect on the state of the program indicates a logic error.
For example, n + 1;
is not a syntax error, but it might be a typing mistake where a programmer meant an assignment statement n += 1;
instead.
Rule Details
This rule aims to eliminate unused expressions which have no effect on the state of the program.
This rule does not apply to function calls or constructor calls with the new
operator, because they could have side effects on the state of the program.
var i = 0;
function increment() { i += 1; }
increment(); // return value is unused, but i changed as a side effect
var nThings = 0;
function Thing() { nThings += 1; }
new Thing(); // constructed object is unused, but nThings changed as a side effect
This rule does not apply to directives (which are in the form of literal string expressions such as "use strict";
at the beginning of a script, module, or function).
Sequence expressions (those using a comma, such as a = 1, b = 2
) are always considered unused unless their return value is assigned or used in a condition evaluation, or a function call is made with the sequence expression value.
Options
This rule, in its default state, does not require any arguments. If you would like to enable one or more of the following you may pass an object with the options set as follows:
-
allowShortCircuit
set totrue
will allow you to use short circuit evaluations in your expressions (Default:false
). -
allowTernary
set totrue
will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default:false
). -
allowTaggedTemplates
set totrue
will enable you to use tagged template literals in your expressions (Default:false
).
These options allow unused expressions only if all of the code paths either directly change the state (for example, assignment statement) or could have side effects (for example, function call).
Examples of incorrect code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
0
if(0) 0
{0}
f(0), {}
a && b()
a, b()
c = a, b;
a() && function namedFunctionInExpressionContext () {f();}
(function anIncompleteIIFE () {});
injectGlobal`body{ color: red; }`
Note that one or more string expression statements (with or without semi-colons) will only be considered as unused if they are not in the beginning of a script, module, or function (alone and uninterrupted by other statements). Otherwise, they will be treated as part of a "directive prologue", a section potentially usable by JavaScript engines. This includes "strict mode" directives.
"use strict";
"use asm"
"use stricter";
"use babel"
"any other strings like this in the prologue";
Examples of correct code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
{} // In this context, this is a block statement, not an object literal
{myLabel: someVar} // In this context, this is a block statement with a label and expression, not an object literal
function namedFunctionDeclaration () {}
(function aGenuineIIFE () {}());
f()
a = 0
new C
delete a.b
void a
allowShortCircuit
Examples of incorrect code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a || b
Examples of correct code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a && b()
a() || (b = c)
allowTernary
Examples of incorrect code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b : 0
a ? b : c()
Examples of correct code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b() : c()
a ? (b = c) : d()
allowShortCircuit and allowTernary
Examples of correct code for the { "allowShortCircuit": true, "allowTernary": true }
options:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true, "allowTernary": true }]*/
a ? b() || (c = d) : e()
allowTaggedTemplates
Examples of incorrect code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
`some untagged template string`;
Examples of correct code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
tag`some tagged template string`;
Source: http://eslint.org/docs/rules/
Expected return with your callback function. Open
if (callback) callback(response, null);
- Read upRead up
- Exclude checks
Enforce Return After Callback (callback-return)
The callback pattern is at the heart of most I/O and event-driven programming in JavaScript.
function doSomething(err, callback) {
if (err) {
return callback(err);
}
callback();
}
To prevent calling the callback multiple times it is important to return
anytime the callback is triggered outside
of the main function body. Neglecting this technique often leads to issues where you do something more than once.
For example, in the case of an HTTP request, you may try to send HTTP headers more than once leading Node.js to throw
a Can't render headers after they are sent to the client.
error.
Rule Details
This rule is aimed at ensuring that callbacks used outside of the main function block are always part-of or immediately
preceding a return
statement. This rule decides what is a callback based on the name of the function being called.
Options
The rule takes a single option - an array of possible callback names - which may include object methods. The default callback names are callback
, cb
, next
.
Default callback names
Examples of incorrect code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err);
}
callback();
}
Examples of correct code for this rule with the default ["callback", "cb", "next"]
option:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
return callback(err);
}
callback();
}
Supplied callback names
Examples of incorrect code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
done(err);
}
done();
}
function bar(err, send) {
if (err) {
send.error(err);
}
send.success();
}
Examples of correct code for this rule with the option ["done", "send.error", "send.success"]
:
/*eslint callback-return: ["error", ["done", "send.error", "send.success"]]*/
function foo(err, done) {
if (err) {
return done(err);
}
done();
}
function bar(err, send) {
if (err) {
return send.error(err);
}
send.success();
}
Known Limitations
Because it is difficult to understand the meaning of a program through static analysis, this rule has limitations:
- false negatives when this rule reports correct code, but the program calls the callback more than one time (which is incorrect behavior)
- false positives when this rule reports incorrect code, but the program calls the callback only one time (which is correct behavior)
Passing the callback by reference
The static analysis of this rule does not detect that the program calls the callback if it is an argument of a function (for example, setTimeout
).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
setTimeout(callback, 0); // this is bad, but WILL NOT warn
}
callback();
}
Triggering the callback within a nested function
The static analysis of this rule does not detect that the program calls the callback from within a nested function or an immediately-invoked function expression (IIFE).
Example of a false negative when this rule reports correct code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
process.nextTick(function() {
return callback(); // this is bad, but WILL NOT warn
});
}
callback();
}
If/else statements
The static analysis of this rule does not detect that the program calls the callback only one time in each branch of an if
statement.
Example of a false positive when this rule reports incorrect code:
/*eslint callback-return: "error"*/
function foo(err, callback) {
if (err) {
callback(err); // this is fine, but WILL warn
} else {
callback(); // this is fine, but WILL warn
}
}
When Not To Use It
There are some cases where you might want to call a callback function more than once. In those cases this rule may lead to incorrect behavior. In those cases you may want to reserve a special name for those callbacks and not include that in the list of callbacks that trigger warnings.
Further Reading
Related Rules
- [handle-callback-err](handle-callback-err.md) Source: http://eslint.org/docs/rules/