eslint/docs/rules/no-constant-condition.md

   1 # disallow constant expressions in conditions (no-constant-condition)
   2
   3 A constant expression (for example, a literal) as a test condition might be a typo or development trigger for a specific behavior. For example, the following code looks as if it is not ready for production.
   4
   5 ```js
   6 if (false) {
   7     doSomethingUnfinished();
   8 }
   9 ```
  10
  11 ## Rule Details
  12
  13 This rule disallows constant expressions in the test condition of:
  14
  15 * `if`, `for`, `while`, or `do...while` statement
  16 * `?:` ternary expression
  17
  18 Examples of **incorrect** code for this rule:
  19
  20 ```js
  21 /*eslint no-constant-condition: "error"*/
  22
  23 if (false) {
  24     doSomethingUnfinished();
  25 }
  26
  27 if (void x) {
  28     doSomethingUnfinished();
  29 }
  30
  31 for (;-2;) {
  32     doSomethingForever();
  33 }
  34
  35 while (typeof x) {
  36     doSomethingForever();
  37 }
  38
  39 do {
  40     doSomethingForever();
  41 } while (x = -1);
  42
  43 var result = 0 ? a : b;
  44 ```
  45
  46 Examples of **correct** code for this rule:
  47
  48 ```js
  49 /*eslint no-constant-condition: "error"*/
  50
  51 if (x === 0) {
  52     doSomething();
  53 }
  54
  55 for (;;) {
  56     doSomethingForever();
  57 }
  58
  59 while (typeof x === "undefined") {
  60     doSomething();
  61 }
  62
  63 do {
  64     doSomething();
  65 } while (x);
  66
  67 var result = x !== 0 ? a : b;
  68 ```
  69
  70 ## Options
  71
  72 ### checkLoops
  73
  74 Set to `true` by default. Setting this option to `false` allows constant expressions in loops.
  75
  76 Examples of **correct** code for when `checkLoops` is `false`:
  77
  78 ```js
  79 /*eslint no-constant-condition: ["error", { "checkLoops": false }]*/
  80
  81 while (true) {
  82     doSomething();
  83     if (condition()) {
  84         break;
  85     }
  86 };
  87
  88 for (;true;) {
  89     doSomething();
  90     if (condition()) {
  91         break;
  92     }
  93 };
  94
  95 do {
  96     doSomething();
  97     if (condition()) {
  98         break;
  99     }
 100 } while (true)
 101 ```