Rediscovering JavaScript: ES6, ES7 & ES8/

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Combining Generators

Combining Generators

Learn how to use yield* to combine generators and iterate over other iterable objects.

We'll cover the following...

In the CardDeck class given in the below code widget, we have two generators:

  1. One to create the suits
  2. The other for pips

It would be a shame if we have to duplicate the code to create a series that contains both suits and pips. Thankfully, we don’t have to endure such pain—JavaScript provides a way to combine generators.

Delegating to already created generator

Let’s create a method, suitsAndPips(), in the CardDeck class.

Javascript (babel-node)
'use strict';
class CardDeck {
  constructor() {
    this.suitShapes = ['Clubs', 'Diamonds', 'Hearts', 'Spaces'];
  }  
   //START:METHOD
  *suits() {
    for(const color of this.suitShapes) {
      yield color;
    }
  }
  //END:METHOD
  //START:PIPS
  *pips() {
    yield 'Ace';
    yield 'King';
    yield 'Queen';
    yield 'Jack';
    
    for(let i = 10; i > 1; i--) {
      yield i.toString();
    }
  }
  //END:PIPS   
  //START:SUITSANDPIPS
  *suitsAndPips() {
    yield* this.suits();
    yield* this.pips();
  }
  //END:SUITSANDPIPS
}
//START:USE
const deck = new CardDeck();
//END:USE
//START:USESUITSANDPIPS
for(const value of deck.suitsAndPips()) {
  process.stdout.write(value + ' ');
}
//END:USESUITSANDPIPS
console.log();

In the suitsAndPips() ...