Learning JavaScript Data Structures and Algorithms - Third Edition

Using map and filter

JavaScript also has two other iterator methods that return a new array with a result. The first one is the map method, which is as follows:

const myMap = numbers.map(isEven); 

The myMap array will have the following values: [false, true, false, true, false, true, false, true, false, true, false, true, false, true, false]. It stores the result of the isEven function that was passed to the map method. This way, we can easily know whether a number is even or not. For example, myMap[0] returns false because 1 is not even, and myMap[1] returns true because 2 is even.

We also have the filter method. It returns a new array with the elements for which the function returned true, as follows:

const evenNumbers = numbers.filter(isEven); ...