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Expected error to be handled. Open
fs.readdir(filename, (err, files) => {
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Enforce Callback Error Handling (handle-callback-err)
In Node.js, a common pattern for dealing with asynchronous behavior is called the callback pattern.
This pattern expects an Error
object or null
as the first argument of the callback.
Forgetting to handle these errors can lead to some really strange behavior in your application.
function loadData (err, data) {
doSomething(); // forgot to handle error
}
Rule Details
This rule expects that when you're using the callback pattern in Node.js you'll handle the error.
Options
The rule takes a single string option: the name of the error parameter. The default is "err"
.
Examples of incorrect code for this rule with the default "err"
parameter name:
/*eslint handle-callback-err: "error"*/
function loadData (err, data) {
doSomething();
}
Examples of correct code for this rule with the default "err"
parameter name:
/*eslint handle-callback-err: "error"*/
function loadData (err, data) {
if (err) {
console.log(err.stack);
}
doSomething();
}
function generateError (err) {
if (err) {}
}
Examples of correct code for this rule with a sample "error"
parameter name:
/*eslint handle-callback-err: ["error", "error"]*/
function loadData (error, data) {
if (error) {
console.log(error.stack);
}
doSomething();
}
regular expression
Sometimes (especially in big projects) the name of the error variable is not consistent across the project, so you need a more flexible configuration to ensure that the rule reports all unhandled errors.
If the configured name of the error variable begins with a ^
it is considered to be a regexp pattern.
- If the option is
"^(err|error|anySpecificError)$"
, the rule reports unhandled errors where the parameter name can beerr
,error
oranySpecificError
. - If the option is
"^.+Error$"
, the rule reports unhandled errors where the parameter name ends withError
(for example,connectionError
orvalidationError
will match). - If the option is
"^.*(e|E)rr"
, the rule reports unhandled errors where the parameter name matches any string that containserr
orErr
(for example,err
,error
,anyError
,some_err
will match).
When Not To Use It
There are cases where it may be safe for your application to ignore errors, however only ignore errors if you are confident that some other form of monitoring will help you catch the problem.
Further Reading
Using width with padding-right can sometimes make elements larger than you expect. Open
padding-right: 30px;
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Rule doesn't have all its properties in alphabetical order. Open
.juicy-spinner-container {
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Unexpected var, use let or const instead. Open
var configuration = {
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidently overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
The following patterns are considered problems:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
The following patterns are not considered problems:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Rule doesn't have all its properties in alphabetical order. Open
.noScroll {
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