extends

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A palavra chave extends é usada em uma class declarations ou class expressions para criar uma classe filha de outra classe.

Sintaxe

class ChildClass extends ParentClass { ... }

Descrição

A palavra chave extends pode ser usada para tanto classes filhas quanto objetos filhos pré-construidos.

O .prototype da extensão deve ser um Object ou null.

Exemplos

Usando extends

O primeiro exemplo cria uma classe chamada Square a partir de uma classe chamada Polygon. Este exemplo foi extraido deste live demo (source).

class Square extends Polygon {
  constructor(length) {
    // Here, it calls the parent class' constructor with lengths
    // provided for the Polygon's width and height
    super(length, length);
    // Note: In derived classes, super() must be called before you
    // can use 'this'. Leaving this out will cause a reference error.
    this.name = 'Square';
  }

  get area() {
    return this.height * this.width;
  }

  set area(value) {
    this.area = value;
  } 
}

Usando extends com objetos pré-construidos

Este exemplo extende o objeto pré-construido Date. Este exemplo foi extraido deste live demo (source).

class myDate extends Date {
  constructor() {
    super();
  }

  getFormattedDate() {
    var months = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'];
    return this.getDate() + "-" + months[this.getMonth()] + "-" + this.getFullYear();
  }
}

Estendendo null

Estender de null funciona como em uma classe normal, exceto que o objeto prototype não herda de Object.prototype.

class nullExtends extends null {
  constructor() {}
}

Object.getPrototypeOf(nullExtends); // Function.prototype
Object.getPrototypeOf(nullExtends.prototype) // null

Especificações

Especificação Status Comentário
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'extends' in that specification.
Padrão Definição inicial.

Compatibilidade com os navegadores

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
extendsChrome Full support 49
Notes
Full support 49
Notes
Notes From Chrome 42 to 48 strict mode is required. Non-strict mode support can be enabled using the flag "Enable Experimental JavaScript".
Edge Full support 13Firefox Full support 45IE No support NoOpera Full support 36
Notes
Full support 36
Notes
Notes From Chrome 29 to 35 strict mode is required. Non-strict mode support can be enabled using the flag "Enable Experimental JavaScript".
Safari Full support 9WebView Android Full support 49
Notes
Full support 49
Notes
Notes From Chrome 42 to 48 strict mode is required. Non-strict mode support can be enabled using the flag "Enable Experimental JavaScript".
Chrome Android Full support 49
Notes
Full support 49
Notes
Notes From Chrome 42 to 48 strict mode is required. Non-strict mode support can be enabled using the flag "Enable Experimental JavaScript".
Firefox Android Full support 45Opera Android Full support 36
Notes
Full support 36
Notes
Notes From Chrome 29 to 35 strict mode is required. Non-strict mode support can be enabled using the flag "Enable Experimental JavaScript".
Safari iOS Full support 9Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
Full support 6.0.0
Full support 4.0.0
Disabled
Disabled From version 4.0.0: this feature is behind the --use_strict runtime flag.
Full support 5.0.0
Disabled
Disabled From version 5.0.0: this feature is behind the --harmony runtime flag.

Legend

Full support  
Full support
No support  
No support
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.

Ver também