Simplifying JavaScript

Tip 6

Check Existence in an Array with Includes()

In this tip, you’ll learn how to find out if a value exists in an array without checking position.

It’s easy to get so caught up in the big exciting changes in a language (such as the spread operator, which you’ll see in a moment) that you miss the small changes that simplify common tasks.

Arrays now have an easy improvement to handle a common problem: testing existence. Testing existence is an important action, and it’s crucial in everything from ternaries (Tip 18, ​ Check Data Quickly with the Ternary Operator ​), to short circuiting (Tip 19, ​ Maximize Efficiency with Short Circuiting ​), to most conditionals in general.

Testing existence with JavaScript arrays has always ...