Learn ECMAScript - Second Edition

The iterable protocol

Any object that implements the iterable protocol is known as an iterable. According to the iterable protocol, an object needs to provide the @@iterator method; that is, it must have the Symbol.iterator symbol as a property key. The @@iterator method must return an iterator object. Here is an example to demonstrate this:

let obj = {  array: [1, 2, 3, 4, 5],  nextIndex: 0,  [Symbol.iterator]: function(){    return {     array: this.array,     nextIndex: this.nextIndex,     next: function(){       return this.nextIndex < this.array.length ?          {value: this.array[this.nextIndex++], done: false} :          {done: true};     }    }  }};let iterable = obj[Symbol.iterator]()console.log(iterable.next().value);console.log(iterable.next().value);console.log(iterable.next().value); ...