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The Complete Guide to Modern JavaScript

What's new in ES2019?

Explore the new features introduced in ES2019 including array flattening with flat and flatMap, creating objects from entries, improved string trimming, optional catch binding, and Symbol descriptions. Understand how these update modern JavaScript to write cleaner, more efficient code.

We'll cover the following...

We’ll look at what’s included in the latest version of ECMAScript: ES2019 in this lesson.

 

Array.prototype.flat() / Array.prototype.flatMap()

Array.prototype.flat() will flatten the array recursively up to the depth that we specify. If no depth argument is specified, 1 is the default value. We can use Infinity to flatten all nested arrays.

Node.js
const letters = ['a', 'b', ['c', 'd', ['e', 'f']]];
// default depth of 1
console.log(letters.flat());
// ['a', 'b', 'c', 'd', ['e', 'f']]
// depth of 2
console.log(letters.flat(2));
// ['a', 'b', 'c', 'd', 'e', 'f']
// which is the same as executing flat with depth of 1 twice
console.log(letters.flat().flat());
// ['a', 'b', 'c', 'd', 'e', 'f']
// Flattens recursively until the array contains no nested arrays
console.log(letters.flat(Infinity));
// ['a', 'b', 'c', 'd', 'e', 'f']

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