Delegation

In the inheritance section we looked at one way to extend a class functionality, there is second way using delegation to extend functionality. With delegation, one object will contain a reference to a different object that it will hand off a request to perform the functionality.

The code below shows how to use delegation with the Bird class and Penguin class. The Penguin class has a reference to the Bird class and it delegates the call made to it's walk method over to Bird's walk method.

  1. // ES6
  2. class Bird {
  3.   constructor(weight, height) {
  4.     this.weight = weight;
  5.     this.height = height;
  6.   }
  7.   walk() {
  8.     console.log('walk!');
  9.   }
  10. }
  12. class Penguin {
  13.   constructor(bird) {
  14.     this.bird = bird;
  15.   }
  16.   walk() {
  17.     this.bird.walk();
  18.   }
  19.   swim() {
  20.     console.log('swim!');
  21.   }
  22. }
  24. const bird = new Bird(...);
  25. const penguin = new Penguin(bird);
  26. penguin.walk(); //walk!
  27. penguin.swim(); //swim!

A good discussion on 'behaviour delegation' can be found here.

原文: https://angular-2-training-book.rangle.io/handout/features/delegation.html