eslint/docs/rules/no-unmodified-loop-condition.md

   1 # Disallow unmodified conditions of loops (no-unmodified-loop-condition)
   2
   3 Variables in a loop condition often are modified in the loop.
   4 If not, it's possibly a mistake.
   5
   6 ```js
   7 while (node) {
   8     doSomething(node);
   9 }
  10 ```
  11
  12 ```js
  13 while (node) {
  14     doSomething(node);
  15     node = node.parent;
  16 }
  17 ```
  18
  19 ## Rule Details
  20
  21 This rule finds references which are inside of loop conditions, then checks the
  22 variables of those references are modified in the loop.
  23
  24 If a reference is inside of a binary expression or a ternary expression, this rule checks the result of
  25 the expression instead.
  26 If a reference is inside of a dynamic expression (e.g. `CallExpression`,
  27 `YieldExpression`, ...), this rule ignores it.
  28
  29 Examples of **incorrect** code for this rule:
  30
  31 ```js
  32 /*eslint no-unmodified-loop-condition: "error"*/
  33
  34 var node = something;
  35
  36 while (node) {
  37     doSomething(node);
  38 }
  39 node = other;
  40
  41 for (var j = 0; j < items.length; ++i) {
  42     doSomething(items[j]);
  43 }
  44
  45 while (node !== root) {
  46     doSomething(node);
  47 }
  48 ```
  49
  50 Examples of **correct** code for this rule:
  51
  52 ```js
  53 /*eslint no-unmodified-loop-condition: "error"*/
  54
  55 while (node) {
  56     doSomething(node);
  57     node = node.parent;
  58 }
  59
  60 for (var j = 0; j < items.length; ++j) {
  61     doSomething(items[j]);
  62 }
  63
  64 // OK, the result of this binary expression is changed in this loop.
  65 while (node !== root) {
  66     doSomething(node);
  67     node = node.parent;
  68 }
  69
  70 // OK, the result of this ternary expression is changed in this loop.
  71 while (node ? A : B) {
  72     doSomething(node);
  73     node = node.parent;
  74 }
  75
  76 // A property might be a getter which has side effect...
  77 // Or "doSomething" can modify "obj.foo".
  78 while (obj.foo) {
  79     doSomething(obj);
  80 }
  81
  82 // A function call can return various values.
  83 while (check(obj)) {
  84     doSomething(obj);
  85 }
  86 ```
  87
  88 ## When Not To Use It
  89
  90 If you don't want to notified about references inside of loop conditions, then it's safe to disable this rule.