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

   1 # Disallow modifying variables that are declared using `const` (no-const-assign)
   2
   3 We cannot modify variables that are declared using `const` keyword.
   4 It will raise a runtime error.
   5
   6 Under non ES2015 environment, it might be ignored merely.
   7
   8 ## Rule Details
   9
  10 This rule is aimed to flag modifying variables that are declared using `const` keyword.
  11
  12 Examples of **incorrect** code for this rule:
  13
  14 ```js
  15 /*eslint no-const-assign: "error"*/
  16 /*eslint-env es6*/
  17
  18 const a = 0;
  19 a = 1;
  20 ```
  21
  22 ```js
  23 /*eslint no-const-assign: "error"*/
  24 /*eslint-env es6*/
  25
  26 const a = 0;
  27 a += 1;
  28 ```
  29
  30 ```js
  31 /*eslint no-const-assign: "error"*/
  32 /*eslint-env es6*/
  33
  34 const a = 0;
  35 ++a;
  36 ```
  37
  38 Examples of **correct** code for this rule:
  39
  40 ```js
  41 /*eslint no-const-assign: "error"*/
  42 /*eslint-env es6*/
  43
  44 const a = 0;
  45 console.log(a);
  46 ```
  47
  48 ```js
  49 /*eslint no-const-assign: "error"*/
  50 /*eslint-env es6*/
  51
  52 for (const a in [1, 2, 3]) { // `a` is re-defined (not modified) on each loop step.
  53     console.log(a);
  54 }
  55 ```
  56
  57 ```js
  58 /*eslint no-const-assign: "error"*/
  59 /*eslint-env es6*/
  60
  61 for (const a of [1, 2, 3]) { // `a` is re-defined (not modified) on each loop step.
  62     console.log(a);
  63 }
  64 ```
  65
  66 ## When Not To Use It
  67
  68 If you don't want to be notified about modifying variables that are declared using `const` keyword, you can safely disable this rule.