eslint/docs/src/rules/constructor-super.md

   1 ---
   2 title: constructor-super
   3 layout: doc
   4 rule_type: problem
   5 ---
   6
   7 Constructors of derived classes must call `super()`.
   8 Constructors of non derived classes must not call `super()`.
   9 If this is not observed, the JavaScript engine will raise a runtime error.
  10
  11 This rule checks whether or not there is a valid `super()` call.
  12
  13 ## Rule Details
  14
  15 This rule is aimed to flag invalid/missing `super()` calls.
  16
  17 Examples of **incorrect** code for this rule:
  18
  19 :::incorrect
  20
  21 ```js
  22 /*eslint constructor-super: "error"*/
  23 /*eslint-env es6*/
  24
  25 class A {
  26     constructor() {
  27         super();  // This is a SyntaxError.
  28     }
  29 }
  30
  31 class A extends B {
  32     constructor() { }  // Would throw a ReferenceError.
  33 }
  34
  35 // Classes which inherits from a non constructor are always problems.
  36 class A extends null {
  37     constructor() {
  38         super();  // Would throw a TypeError.
  39     }
  40 }
  41
  42 class A extends null {
  43     constructor() { }  // Would throw a ReferenceError.
  44 }
  45 ```
  46
  47 :::
  48
  49 Examples of **correct** code for this rule:
  50
  51 :::correct
  52
  53 ```js
  54 /*eslint constructor-super: "error"*/
  55 /*eslint-env es6*/
  56
  57 class A {
  58     constructor() { }
  59 }
  60
  61 class A extends B {
  62     constructor() {
  63         super();
  64     }
  65 }
  66 ```
  67
  68 :::
  69
  70 ## When Not To Use It
  71
  72 If you don't want to be notified about invalid/missing `super()` callings in constructors, you can safely disable this rule.