eslint/docs/rules/no-multi-assign.md

   1 # Disallow Use of Chained Assignment Expressions (no-multi-assign)
   2
   3 Chaining the assignment of variables can lead to unexpected results and be difficult to read.
   4
   5 ```js
   6 (function() {
   7     const foo = bar = 0; // Did you mean `foo = bar == 0`?
   8     bar = 1;             // This will not fail since `bar` is not constant.
   9 })();
  10 console.log(bar);        // This will output 1 since `bar` is not scoped.
  11 ```
  12
  13 ## Rule Details
  14
  15 This rule disallows using multiple assignments within a single statement.
  16
  17 Examples of **incorrect** code for this rule:
  18
  19 ```js
  20 /*eslint no-multi-assign: "error"*/
  21
  22 var a = b = c = 5;
  23
  24 const foo = bar = "baz";
  25
  26 let a =
  27     b =
  28     c;
  29 ```
  30
  31 Examples of **correct** code for this rule:
  32
  33 ```js
  34 /*eslint no-multi-assign: "error"*/
  35 var a = 5;
  36 var b = 5;
  37 var c = 5;
  38
  39 const foo = "baz";
  40 const bar = "baz";
  41
  42 let a = c;
  43 let b = c;
  44 ```
  45
  46 ## Options
  47
  48 This rule has an object option:
  49
  50 * `"ignoreNonDeclaration"`: When set to `true`, the rule allows chains that don't include initializing a variable in a declaration. Default is `false`.
  51
  52 ### ignoreNonDeclaration
  53
  54 Examples of **correct** code for the `{ "ignoreNonDeclaration": true }` option:
  55
  56 ```js
  57 /*eslint no-multi-assign: ["error", { "ignoreNonDeclaration": true }]*/
  58
  59 let a;
  60 let b;
  61 a = b = "baz";
  62
  63 const x = {};
  64 const y = {};
  65 x.one = y.one = 1;
  66 ```
  67
  68 Examples of **incorrect** code for the `{ "ignoreNonDeclaration": true }` option:
  69
  70 ```js
  71 /*eslint no-multi-assign: ["error", { "ignoreNonDeclaration": true }]*/
  72
  73 let a = b = "baz";
  74
  75 const foo = bar = 1;
  76 ```
  77
  78 ## Related Rules
  79
  80 * [max-statements-per-line](max-statements-per-line.md)