map() is key method of an array when it comes to thinking in functional programming terms.
This example iterates
a and builds a new array with the result of executing
f() on each
const b = a.map(f)
Given an array, we can use
map() to create a new array from the initial one, and then filtering the result using
filter(). This short example creates a new array to get the first letter of each item in the
list array, and filters the one that matches
const list = ['Apple', 'Orange', 'Egg'] list.map(item => item).filter(item => item === 'A') //'A'