Mastering JavaScript Functional Programming - Second Edition

Flattening an array

In ES2019, two operations were added to JavaScript: flat(), which we'll look at now, and flatMap(), which we'll look at a bit later. It's easier to show what they do than to explain—bear with me!

As often happens, not all browsers have been updated to include these new methods, and Microsoft's Internet Explorer and Edge (among others) are both deficient in this regard, so for web programming, you'll probably have to include a polyfill, or use some kind of implementation, which we'll be learning about soon. As usual, for updated compatibility data, check out the Can I use? site, in this case, at https://caniuse.com/#feat=array-flat.

The flat() method creates a new array, concatenating all elements of its subarrays to the ...