huridocs/uwazi

title: prefer-promise-reject-errors ruletype: suggestion relatedrules: - no-throw-literal further_reading:

- http://bluebirdjs.com/docs/warning-explanations.html#warning-a-promise-was-rejected-with-a-non-error

It is considered good practice to only pass instances of the built-in Error object to the reject() function for user-defined errors in Promises. Error objects automatically store a stack trace, which can be used to debug an error by determining where it came from. If a Promise is rejected with a non-Error value, it can be difficult to determine where the rejection occurred.

Rule Details

This rule aims to ensure that Promises are only rejected with Error objects.

Options

This rule takes one optional object argument:

• allowEmptyReject: true (false by default) allows calls to Promise.reject() with no arguments.

Examples of incorrect code for this rule:

::: incorrect

/*eslint prefer-promise-reject-errors: "error"*/

Promise.reject("something bad happened");

Promise.reject(5);

Promise.reject();

new Promise(function(resolve, reject) {
  reject("something bad happened");
});

new Promise(function(resolve, reject) {
  reject();
});

:::

Examples of correct code for this rule:

::: correct

/*eslint prefer-promise-reject-errors: "error"*/

Promise.reject(new Error("something bad happened"));

Promise.reject(new TypeError("something bad happened"));

new Promise(function(resolve, reject) {
  reject(new Error("something bad happened"));
});

var foo = getUnknownValue();
Promise.reject(foo);

:::

Examples of correct code for this rule with the allowEmptyReject: true option:

::: correct

/*eslint prefer-promise-reject-errors: ["error", {"allowEmptyReject": true}]*/

Promise.reject();

new Promise(function(resolve, reject) {
  reject();
});

:::

Known Limitations

Due to the limits of static analysis, this rule cannot guarantee that you will only reject Promises with Error objects. While the rule will report cases where it can guarantee that the rejection reason is clearly not an Error, it will not report cases where there is uncertainty about whether a given reason is an Error. For more information on this caveat, see the [similar limitations](no-throw-literal#known-limitations) in the no-throw-literal rule.

To avoid conflicts between rules, this rule does not report non-error values used in throw statements in async functions, even though these lead to Promise rejections. To lint for these cases, use the [no-throw-literal](no-throw-literal) rule.

When Not To Use It

If you're using custom non-error values as Promise rejection reasons, you can turn off this rule. Source: http://eslint.org/docs/rules/

title: consistent-return

rule_type: suggestion

Unlike statically-typed languages which enforce that a function returns a specified type of value, JavaScript allows different code paths in a function to return different types of values.

A confusing aspect of JavaScript is that a function returns undefined if any of the following are true:

• it does not execute a return statement before it exits
• it executes return which does not specify a value explicitly
• it executes return undefined
• it executes return void followed by an expression (for example, a function call)
• it executes return followed by any other expression which evaluates to undefined

If any code paths in a function return a value explicitly but some code path do not return a value explicitly, it might be a typing mistake, especially in a large function. In the following example:

• a code path through the function returns a Boolean value true
• another code path does not return a value explicitly, therefore returns undefined implicitly

function doSomething(condition) {
    if (condition) {
        return true;
    } else {
        return;
    }
}

Rule Details

This rule requires return statements to either always or never specify values. This rule ignores function definitions where the name begins with an uppercase letter, because constructors (when invoked with the new operator) return the instantiated object implicitly if they do not return another object explicitly.

Examples of incorrect code for this rule:

::: incorrect

/*eslint consistent-return: "error"*/

function doSomething(condition) {
    if (condition) {
        return true;
    } else {
        return;
    }
}

function doSomething(condition) {
    if (condition) {
        return true;
    }
}

:::

Examples of correct code for this rule:

::: correct

/*eslint consistent-return: "error"*/

function doSomething(condition) {
    if (condition) {
        return true;
    } else {
        return false;
    }
}

function Foo() {
    if (!(this instanceof Foo)) {
        return new Foo();
    }

    this.a = 0;
}

:::

Options

This rule has an object option:

• "treatUndefinedAsUnspecified": false (default) always either specify values or return undefined implicitly only.
• "treatUndefinedAsUnspecified": true always either specify values or return undefined explicitly or implicitly.

treatUndefinedAsUnspecified

Examples of incorrect code for this rule with the default { "treatUndefinedAsUnspecified": false } option:

::: incorrect

/*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": false }]*/

function foo(callback) {
    if (callback) {
        return void callback();
    }
    // no return statement
}

function bar(condition) {
    if (condition) {
        return undefined;
    }
    // no return statement
}

:::

Examples of incorrect code for this rule with the { "treatUndefinedAsUnspecified": true } option:

::: incorrect

/*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/

function foo(callback) {
    if (callback) {
        return void callback();
    }
    return true;
}

function bar(condition) {
    if (condition) {
        return undefined;
    }
    return true;
}

:::

Examples of correct code for this rule with the { "treatUndefinedAsUnspecified": true } option:

::: correct

/*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/

function foo(callback) {
    if (callback) {
        return void callback();
    }
    // no return statement
}

function bar(condition) {
    if (condition) {
        return undefined;
    }
    // no return statement
}

:::

When Not To Use It

If you want to allow functions to have different return behavior depending on code branching, then it is safe to disable this rule. Source: http://eslint.org/docs/rules/

title: no-param-reassign ruletype: suggestion furtherreading:

- https://spin.atomicobject.com/2011/04/10/javascript-don-t-reassign-your-function-arguments/

Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object when not in strict mode (see When Not To Use It below). Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.

This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.

Rule Details

This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.

Examples of incorrect code for this rule:

::: incorrect

/*eslint no-param-reassign: "error"*/

function foo(bar) {
    bar = 13;
}

function foo(bar) {
    bar++;
}

function foo(bar) {
    for (bar in baz) {}
}

function foo(bar) {
    for (bar of baz) {}
}

:::

Examples of correct code for this rule:

::: correct

/*eslint no-param-reassign: "error"*/

function foo(bar) {
    var baz = bar;
}

:::

Options

This rule takes one option, an object, with a boolean property "props", and arrays "ignorePropertyModificationsFor" and "ignorePropertyModificationsForRegex". "props" is false by default. If "props" is set to true, this rule warns against the modification of parameter properties unless they're included in "ignorePropertyModificationsFor" or "ignorePropertyModificationsForRegex", which is an empty array by default.

props

Examples of correct code for the default { "props": false } option:

::: correct

/*eslint no-param-reassign: ["error", { "props": false }]*/

function foo(bar) {
    bar.prop = "value";
}

function foo(bar) {
    delete bar.aaa;
}

function foo(bar) {
    bar.aaa++;
}

function foo(bar) {
    for (bar.aaa in baz) {}
}

function foo(bar) {
    for (bar.aaa of baz) {}
}

:::

Examples of incorrect code for the { "props": true } option:

::: incorrect

/*eslint no-param-reassign: ["error", { "props": true }]*/

function foo(bar) {
    bar.prop = "value";
}

function foo(bar) {
    delete bar.aaa;
}

function foo(bar) {
    bar.aaa++;
}

function foo(bar) {
    for (bar.aaa in baz) {}
}

function foo(bar) {
    for (bar.aaa of baz) {}
}

:::

Examples of correct code for the { "props": true } option with "ignorePropertyModificationsFor" set:

::: correct

/*eslint no-param-reassign: ["error", { "props": true, "ignorePropertyModificationsFor": ["bar"] }]*/

function foo(bar) {
    bar.prop = "value";
}

function foo(bar) {
    delete bar.aaa;
}

function foo(bar) {
    bar.aaa++;
}

function foo(bar) {
    for (bar.aaa in baz) {}
}

function foo(bar) {
    for (bar.aaa of baz) {}
}

:::

Examples of correct code for the { "props": true } option with "ignorePropertyModificationsForRegex" set:

::: correct

/*eslint no-param-reassign: ["error", { "props": true, "ignorePropertyModificationsForRegex": ["^bar"] }]*/

function foo(barVar) {
    barVar.prop = "value";
}

function foo(barrito) {
    delete barrito.aaa;
}

function foo(bar_) {
    bar_.aaa++;
}

function foo(barBaz) {
    for (barBaz.aaa in baz) {}
}

function foo(barBaz) {
    for (barBaz.aaa of baz) {}
}

:::

When Not To Use It

If you want to allow assignment to function parameters, then you can safely disable this rule.

Strict mode code doesn't sync indices of the arguments object with each parameter binding. Therefore, this rule is not necessary to protect against arguments object mutation in ESM modules or other strict mode functions. Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/