eslint/docs/src/rules/no-this-before-super.md

   1 ---
   2 title: no-this-before-super
   3 rule_type: problem
   4 ---
   5
   6
   7
   8 In the constructor of derived classes, if `this`/`super` are used before `super()` calls, it raises a reference error.
   9
  10 This rule checks `this`/`super` keywords in constructors, then reports those that are before `super()`.
  11
  12 ## Rule Details
  13
  14 This rule is aimed to flag `this`/`super` keywords before `super()` callings.
  15
  16 ## Examples
  17
  18 Examples of **incorrect** code for this rule:
  19
  20 ::: incorrect
  21
  22 ```js
  23 /*eslint no-this-before-super: "error"*/
  24 /*eslint-env es6*/
  25
  26 class A extends B {
  27     constructor() {
  28         this.a = 0;
  29         super();
  30     }
  31 }
  32
  33 class A extends B {
  34     constructor() {
  35         this.foo();
  36         super();
  37     }
  38 }
  39
  40 class A extends B {
  41     constructor() {
  42         super.foo();
  43         super();
  44     }
  45 }
  46
  47 class A extends B {
  48     constructor() {
  49         super(this.foo());
  50     }
  51 }
  52 ```
  53
  54 :::
  55
  56 Examples of **correct** code for this rule:
  57
  58 ::: correct
  59
  60 ```js
  61 /*eslint no-this-before-super: "error"*/
  62 /*eslint-env es6*/
  63
  64 class A {
  65     constructor() {
  66         this.a = 0; // OK, this class doesn't have an `extends` clause.
  67     }
  68 }
  69
  70 class A extends B {
  71     constructor() {
  72         super();
  73         this.a = 0; // OK, this is after `super()`.
  74     }
  75 }
  76
  77 class A extends B {
  78     foo() {
  79         this.a = 0; // OK. this is not in a constructor.
  80     }
  81 }
  82 ```
  83
  84 :::
  85
  86 ## When Not To Use It
  87
  88 If you don't want to be notified about using `this`/`super` before `super()` in constructors, you can safely disable this rule.