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This is a new technology, part of the ECMAScript 2015 (ES6) standard .
This technology's specification has been finalized, but check the compatibility table for usage and implementation status in various browsers.
The constructor method is a special method for creating and initializing an object created with a class.
Syntax
constructor([arguments]) { ... }
Description
There can only be one special method with the name "constructor" in a class. A SyntaxError will be thrown, if the class contains more than one occurrence of a constructor method.
A constructor can use the super keyword to call the constructor of a parent class.
Examples
This code snippet is taken from the classes sample (live demo).
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;
}
}
Specifications
| Specification | Status | Comment |
|---|---|---|
| ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Constructor Method' in that specification. |
Standard | Initial definition. |
Browser compatibility
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 42.0 | Nightly build | ? | ? | ? |
| Feature | Android | Android Webview | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
|---|---|---|---|---|---|---|---|
| Basic support | Not supported | 42.0 | Nightly build | ? | ? | ? | 42.0 |
Firefox-specific notes
- Default constructors are not implemented yet (bug 1105463)