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

   1 # Disallow Self Assignment (no-self-assign)
   2
   3 Self assignments have no effect, so probably those are an error due to incomplete refactoring.
   4 Those indicate that what you should do is still remaining.
   5
   6 ```js
   7 foo = foo;
   8 [bar, baz] = [bar, qiz];
   9 ```
  10
  11 ## Rule Details
  12
  13 This rule is aimed at eliminating self assignments.
  14
  15 Examples of **incorrect** code for this rule:
  16
  17 ```js
  18 /*eslint no-self-assign: "error"*/
  19
  20 foo = foo;
  21
  22 [a, b] = [a, b];
  23
  24 [a, ...b] = [x, ...b];
  25
  26 ({a, b} = {a, x});
  27 ```
  28
  29 Examples of **correct** code for this rule:
  30
  31 ```js
  32 /*eslint no-self-assign: "error"*/
  33
  34 foo = bar;
  35 [a, b] = [b, a];
  36
  37 // This pattern is warned by the `no-use-before-define` rule.
  38 let foo = foo;
  39
  40 // The default values have an effect.
  41 [foo = 1] = [foo];
  42
  43 // non-self-assignments with properties.
  44 obj.a = obj.b;
  45 obj.a.b = obj.c.b;
  46 obj.a.b = obj.a.c;
  47 obj[a] = obj["a"];
  48
  49 // This ignores if there is a function call.
  50 obj.a().b = obj.a().b;
  51 a().b = a().b;
  52
  53 // Known limitation: this does not support computed properties except single literal or single identifier.
  54 obj[a + b] = obj[a + b];
  55 obj["a" + "b"] = obj["a" + "b"];
  56 ```
  57
  58 ## Options
  59
  60 This rule has the option to check properties as well.
  61
  62 ```json
  63 {
  64     "no-self-assign": ["error", {"props": true}]
  65 }
  66 ```
  67
  68 - `props` - if this is `true`, `no-self-assign` rule warns self-assignments of properties. Default is `true`.
  69
  70 ### props
  71
  72 Examples of **correct** code with the `{ "props": false }` option:
  73
  74 ```js
  75 /*eslint no-self-assign: ["error", {"props": false}]*/
  76
  77 // self-assignments with properties.
  78 obj.a = obj.a;
  79 obj.a.b = obj.a.b;
  80 obj["a"] = obj["a"];
  81 obj[a] = obj[a];
  82 ```
  83
  84 ## When Not To Use It
  85
  86 If you don't want to notify about self assignments, then it's safe to disable this rule.