eslint/docs/rules/no-unneeded-ternary.md

   1 # disallow ternary operators when simpler alternatives exist (no-unneeded-ternary)
   2
   3 It's a common mistake in JavaScript to use a conditional expression to select between two Boolean values instead of using ! to convert the test to a Boolean.
   4 Here are some examples:
   5
   6 ```js
   7 // Bad
   8 var isYes = answer === 1 ? true : false;
   9
  10 // Good
  11 var isYes = answer === 1;
  12
  13
  14 // Bad
  15 var isNo = answer === 1 ? false : true;
  16
  17 // Good
  18 var isNo = answer !== 1;
  19 ```
  20
  21 Another common mistake is using a single variable as both the conditional test and the consequent. In such cases, the logical `OR` can be used to provide the same functionality.
  22 Here is an example:
  23
  24 ```js
  25 // Bad
  26 foo(bar ? bar : 1);
  27
  28 // Good
  29 foo(bar || 1);
  30 ```
  31
  32 ## Rule Details
  33
  34 This rule disallow ternary operators when simpler alternatives exist.
  35
  36 Examples of **incorrect** code for this rule:
  37
  38 ```js
  39 /*eslint no-unneeded-ternary: "error"*/
  40
  41 var a = x === 2 ? true : false;
  42
  43 var a = x ? true : false;
  44 ```
  45
  46 Examples of **correct** code for this rule:
  47
  48 ```js
  49 /*eslint no-unneeded-ternary: "error"*/
  50
  51 var a = x === 2 ? "Yes" : "No";
  52
  53 var a = x !== false;
  54
  55 var a = x ? "Yes" : "No";
  56
  57 var a = x ? y : x;
  58
  59 f(x ? x : 1); // default assignment - would be disallowed if defaultAssignment option set to false. See option details below.
  60 ```
  61
  62 ## Options
  63
  64 This rule has an object option:
  65
  66 * `"defaultAssignment": true` (default) allows the conditional expression as a default assignment pattern
  67 * `"defaultAssignment": false` disallows the conditional expression as a default assignment pattern
  68
  69 ### defaultAssignment
  70
  71 When set to `true`, which it is by default, The defaultAssignment option allows expressions of the form `x ? x : expr` (where `x` is any identifier and `expr` is any expression).
  72
  73 Examples of additional **incorrect** code for this rule with the `{ "defaultAssignment": false }` option:
  74
  75 ```js
  76 /*eslint no-unneeded-ternary: ["error", { "defaultAssignment": false }]*/
  77
  78 var a = x ? x : 1;
  79
  80 f(x ? x : 1);
  81 ```
  82
  83 Note that `defaultAssignment: false` still allows expressions of the form `x ? expr : x` (where the identifier is on the right hand side of the ternary).
  84
  85 ## When Not To Use It
  86
  87 You can turn this rule off if you are not concerned with unnecessary complexity in conditional expressions.
  88
  89 ## Related Rules
  90
  91 * [no-ternary](no-ternary.md)
  92 * [no-nested-ternary](no-nested-ternary.md)