Simplifying JavaScript

Tip 26

Transform Array Data with reduce()

In this tip, you’ll learn how use reduce() to generate a new array with a different size and shape.

You’re probably tired of hearing me say that good code is predictable. But it’s true. Array methods are wonderful because you have an idea of the result at a glance without even understanding the callback function. Not only that, but array methods are easier to test and, as you’ll see in Tip 32, ​Write Functions for Testability ​, it’s much easier to write testable code than it is to add tests to complex code.

Still, there are times when you need to create a new, radically different piece of data from an array. Maybe you need to get a count of certain items. Maybe you want to transform the ...