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# Convert Iterables to Array using Spread

Use ES6 spread (...) to easily convert Iterables into an Array! Often, iterables are limited in terms of their built-in methods. By converting it into an array, you'll have access to ALL of the amazing array methods such as filter, map, reduce! Awesome 🎉

[ ...'hi' ]; // // ['h', 'i']

[ ...new Set([1,2,3]) ]; // [1,2,3]

[ ...new Map([[1, 'one']]) ]; // [[1, 'one']]

[ ...document.querySelectorAll('div') ] // [ div, div, div]

# Built-in Iterables

In JavaScript, we have some built-in iterables that we use spread to convert them to an array:

  • String
  • Array
  • Map
  • Set

There's one more, but we won't focus on that for this post, TypedArray.

# What are Iterables?

Iterables are data structures which provide a mechanism to allow other data consumers to publicly access its elements in a sequential manner.

If you're interested in learning more about iterables, check out these awesome posts:

# String → Array

const myString = 'hello';

const array = [...myString] // [ 'h', 'e', 'l', 'l', 'o' ]

We can convert the array back to a string by using join()

array.join(''); // 'hello'

# Set → Array

const mySet = new Set([1, 2, 3]);

const array = [...mySet] // [1, 2, 3]

We can convert the array back to a string by passing it into new Set

new Set(array); // Set { 1, 2, 3 }

# Map → Array

const myMap = new Map([[1, 'one'], [2, 'two']]);

const array = [...myMap] // [ [ 1, 'one' ], [ 2, 'two' ] ]

Similar to Set, we can convert the array back to a string by passing it into new Map

new Map(array); // Map { 1 => 'one', 2 => 'two' }

# NodeList → Array

const nodeList = document.querySelectorAll('div');

const array = [ ...document.querySelectorAll('div') ];
// [ div, div, div] *

*I suggest you paste the code into your browser to see the actual output

# Array.from vs Spread

Another very similar method to the Spread syntax is Array.from. In fact, we can replace our examples with this:

Array.from('hi') // // ['h', 'i']

Array.from(new Set([1,2,3])) // [1,2,3]

Array.from(new Map([[1, 'one']])) // [[1, 'one']]

Array.from(document.querySelectorAll('div')) // [ div, div, div]

# What's the difference?

The difference is in the definition

Array.from works for:

  • array-like objects (objects with a length property and indexed elements)
  • iterable objects

Spread only works for:

  • iterable objects

So let's take a look at this array-like object:

const arrayLikeObject = {
  0: 'a', // indexed element
  1: 'b', // indexed element
  length: 1, // length property

// ✅ Using Array.from
Array.from(arrayLikeObject); // [ 'a', 'b' ]

// ❌ Using Spread
[...arrayLikeObject]; // TypeError: arrayLikeObject is not iterable

# Which should I use?

Of course, it depends. If you are working with array-like objects, you have no choice but to use Array.from. But when it comes to iterables, I've always used spreads. Why? Because I'm a huge fan of the Airbnb Style guide. I wish I have a better reason, but that's all I have lol 😝 I'm guessing because it's less typing 🤔 If you know the reason, please drop it in the comment 😆

# Community Input

@nickytonline: I like using spread as well, but if you want to e.g. convert a NodeList to an array and then map over it, consider using Array.from. I discovered this summer that Array.from has a second argument which is a map callback function that is called as each item is created.

# Resources

Related Tidbits