eslint/docs/src/rules/no-eq-null.md

   1 ---
   2 title: no-eq-null
   3 rule_type: suggestion
   4 ---
   5
   6
   7 Comparing to `null` without a type-checking operator (`==` or `!=`), can have unintended results as the comparison will evaluate to true when comparing to not just a `null`, but also an `undefined` value.
   8
   9 ```js
  10 if (foo == null) {
  11   bar();
  12 }
  13 ```
  14
  15 ## Rule Details
  16
  17 The `no-eq-null` rule aims reduce potential bug and unwanted behavior by ensuring that comparisons to `null` only match `null`, and not also `undefined`. As such it will flag comparisons to null when using `==` and `!=`.
  18
  19 Examples of **incorrect** code for this rule:
  20
  21 ::: incorrect
  22
  23 ```js
  24 /*eslint no-eq-null: "error"*/
  25
  26 if (foo == null) {
  27   bar();
  28 }
  29
  30 while (qux != null) {
  31   baz();
  32 }
  33 ```
  34
  35 :::
  36
  37 Examples of **correct** code for this rule:
  38
  39 ::: correct
  40
  41 ```js
  42 /*eslint no-eq-null: "error"*/
  43
  44 if (foo === null) {
  45   bar();
  46 }
  47
  48 while (qux !== null) {
  49   baz();
  50 }
  51 ```
  52
  53 :::
  54
  55 ## When Not To Use It
  56
  57 If you want to enforce type-checking operations in general, use the more powerful [eqeqeq](./eqeqeq) instead.
  58
  59 ## Compatibility
  60
  61 * **JSHint**: This rule corresponds to `eqnull` rule of JSHint.