eslint/docs/src/rules/no-native-reassign.md

   1 ---
   2 title: no-native-reassign
   3 layout: doc
   4 rule_type: suggestion
   5 related_rules:
   6 - no-extend-native
   7 - no-redeclare
   8 - no-shadow
   9 ---
  10
  11
  12 This rule was **deprecated** in ESLint v3.3.0 and replaced by the [no-global-assign](no-global-assign) rule.
  13
  14 JavaScript environments contain a number of built-in global variables, such as `window` in browsers and `process` in Node.js. In almost all cases, you don't want to assign a value to these global variables as doing so could result in losing access to important functionality. For example, you probably don't want to do this in browser code:
  15
  16 ```js
  17 window = {};
  18 ```
  19
  20 While examples such as `window` are obvious, there are often hundreds of built-in global objects provided by JavaScript environments. It can be hard to know if you're assigning to a global variable or not.
  21
  22 ## Rule Details
  23
  24 This rule disallows modifications to read-only global variables.
  25
  26 ESLint has the capability to configure global variables as read-only.
  27
  28 * [Specifying Environments](../user-guide/configuring#specifying-environments)
  29 * [Specifying Globals](../user-guide/configuring#specifying-globals)
  30
  31 Examples of **incorrect** code for this rule:
  32
  33 ::: incorrect
  34
  35 ```js
  36 /*eslint no-native-reassign: "error"*/
  37
  38 Object = null
  39 undefined = 1
  40 ```
  41
  42 :::
  43
  44 ::: incorrect
  45
  46 ```js
  47 /*eslint no-native-reassign: "error"*/
  48 /*eslint-env browser*/
  49
  50 window = {}
  51 length = 1
  52 top = 1
  53 ```
  54
  55 :::
  56
  57 ::: incorrect
  58
  59 ```js
  60 /*eslint no-native-reassign: "error"*/
  61 /*global a:readonly*/
  62
  63 a = 1
  64 ```
  65
  66 :::
  67
  68 Examples of **correct** code for this rule:
  69
  70 ::: correct
  71
  72 ```js
  73 /*eslint no-native-reassign: "error"*/
  74
  75 a = 1
  76 var b = 1
  77 b = 2
  78 ```
  79
  80 :::
  81
  82 ::: correct
  83
  84 ```js
  85 /*eslint no-native-reassign: "error"*/
  86 /*eslint-env browser*/
  87
  88 onload = function() {}
  89 ```
  90
  91 :::
  92
  93 ::: correct
  94
  95 ```js
  96 /*eslint no-native-reassign: "error"*/
  97 /*global a:writable*/
  98
  99 a = 1
 100 ```
 101
 102 :::
 103
 104 ## Options
 105
 106 This rule accepts an `exceptions` option, which can be used to specify a list of builtins for which reassignments will be allowed:
 107
 108 ```json
 109 {
 110     "rules": {
 111         "no-native-reassign": ["error", {"exceptions": ["Object"]}]
 112     }
 113 }
 114 ```
 115
 116 ## When Not To Use It
 117
 118 If you are trying to override one of the native objects.