eslint/docs/rules/consistent-this.md

   1 # Require Consistent This (consistent-this)
   2
   3 It is often necessary to capture the current execution context in order to make it available subsequently. A prominent example of this are jQuery callbacks:
   4
   5 ```js
   6 var that = this;
   7 jQuery('li').click(function (event) {
   8     // here, "this" is the HTMLElement where the click event occurred
   9     that.setFoo(42);
  10 });
  11 ```
  12
  13 There are many commonly used aliases for `this` such as `that`, `self` or `me`. It is desirable to ensure that whichever alias the team agrees upon is used consistently throughout the application.
  14
  15 ## Rule Details
  16
  17 This rule enforces two things about variables with the designated alias names for `this`:
  18
  19 * If a variable with a designated name is declared, it *must* be either initialized (in the declaration) or assigned (in the same scope as the declaration) the value `this`.
  20 * If a variable is initialized or assigned the value `this`, the name of the variable *must* be a designated alias.
  21
  22 ## Options
  23
  24 This rule has one or more string options:
  25
  26 * designated alias names for `this` (default `"that"`)
  27
  28 Examples of **incorrect** code for this rule with the default `"that"` option:
  29
  30 ```js
  31 /*eslint consistent-this: ["error", "that"]*/
  32
  33 var that = 42;
  34
  35 var self = this;
  36
  37 that = 42;
  38
  39 self = this;
  40 ```
  41
  42 Examples of **correct** code for this rule with the default `"that"` option:
  43
  44 ```js
  45 /*eslint consistent-this: ["error", "that"]*/
  46
  47 var that = this;
  48
  49 var self = 42;
  50
  51 var self;
  52
  53 that = this;
  54
  55 foo.bar = this;
  56 ```
  57
  58 Examples of **incorrect** code for this rule with the default `"that"` option, if the variable is not initialized:
  59
  60 ```js
  61 /*eslint consistent-this: ["error", "that"]*/
  62
  63 var that;
  64 function f() {
  65     that = this;
  66 }
  67 ```
  68
  69 Examples of **correct** code for this rule with the default `"that"` option, if the variable is not initialized:
  70
  71 ```js
  72 /*eslint consistent-this: ["error", "that"]*/
  73
  74 var that;
  75 that = this;
  76
  77 var foo, that;
  78 foo = 42;
  79 that = this;
  80 ```
  81
  82 ## When Not To Use It
  83
  84 If you need to capture nested context, `consistent-this` is going to be problematic. Code of that nature is usually difficult to read and maintain and you should consider refactoring it.