Iterable : Object

An iterable object is any object that has a Symbol.iterator property whose value is a function that returns an Iterator.

You can loop over all values in an iterable object by using a for (const value of iterable) { } loop.

You may create your own iterable object by assigning the Symbol.iterator property to a generator function (function* () {}) or an object with a next() method.

See Iterator for more details.

ECMAScript 2015 Spec

Instance Indexers

this[Symbol.iterator] : Function<Iterator>

Returns a function that produces an Iterator for this object.

Example:

// Arrays are a built in Iterable object
const arr = ['a', 'b', 'c'];

// Use for (... of ...) loop to get the values of an iterable
for (const x of arr) {
  console.log(x);
} 

// Create an iterable class with a generator function
class MyIterable {
  constructor(maxValue) {
    this._maxValue = maxValue;
  }

  *[Symbol.iterator]() {
    for (let i = 0; i < this._maxValue; i++) {
      yield i;
    }
  }
}

for (const x of new MyIterable(3)) {
  console.log(x);
}

// Under the covers, for (... of ...) does the following: 
const iterator = arr[Symbol.iterator]();
let current = iterator.next();
while (!current.done) {
  console.log(current.value);
  current = iterator.next();
}

Run

Results:

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