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no-confusing-arrow

Disallow arrow functions where they could be confused with comparisons

🔧 Fixable

Some problems reported by this rule are automatically fixable by the --fix command line option

Arrow functions (=>) are similar in syntax to some comparison operators (>, <, <=, and >=). This rule warns against using the arrow function syntax in places where it could be confused with a comparison operator.

Here’s an example where the usage of => could be confusing:

// The intent is not clear
var x = a => 1 ? 2 : 3;
// Did the author mean this
var x = function (a) {
return 1 ? 2 : 3;
};
// Or this
var x = a <= 1 ? 2 : 3;

Rule Details

Examples of incorrect code for this rule:

/*eslint no-confusing-arrow: "error"*/
/*eslint-env es6*/

var x = a => 1 ? 2 : 3;
var x = (a) => 1 ? 2 : 3;

Examples of correct code for this rule:

/*eslint no-confusing-arrow: "error"*/
/*eslint-env es6*/
var x = a => (1 ? 2 : 3);
var x = (a) => (1 ? 2 : 3);
var x = (a) => {
return 1 ? 2 : 3;
};
var x = a => { return 1 ? 2 : 3; };

Options

This rule accepts two options argument with the following defaults:

{
"rules": {
"no-confusing-arrow": [
"error",
{ "allowParens": true, "onlyOneSimpleParam": false }
]
}
}

allowParens is a boolean setting that can be true(default) or false:

  1. true relaxes the rule and accepts parenthesis as a valid “confusion-preventing” syntax.
  2. false warns even if the expression is wrapped in parenthesis

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

/*eslint no-confusing-arrow: ["error", {"allowParens": false}]*/
/*eslint-env es6*/
var x = a => (1 ? 2 : 3);
var x = (a) => (1 ? 2 : 3);

onlyOneSimpleParam is a boolean setting that can be true or false(default):

  1. true relaxes the rule and doesn’t report errors if the arrow function has 0 or more than 1 parameters, or the parameter is not an identifier.
  2. false warns regardless of parameters.

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

/*eslint no-confusing-arrow: ["error", {"onlyOneSimpleParam": true}]*/
/*eslint-env es6*/
() => 1 ? 2 : 3;
(a, b) => 1 ? 2 : 3;
(a = b) => 1 ? 2 : 3;
({ a }) => 1 ? 2 : 3;
([a]) => 1 ? 2 : 3;
(...a) => 1 ? 2 : 3;

Version

This rule was introduced in ESLint v2.0.0-alpha-2.

Resources