Array.prototype functional methods

file.js

let arr = [1, 2, 3];

function log(item) {
    console.log(item);
}

//forEach performs an action on each item 
//in an array

arr.forEach(log); //logs 1 2 3 in order

function increment(num) {
    return num + 1;
}

//map transforms each item in an array and 
//returns  new array with the transformed 
//values leaving the original unchanged
arr.map(increment) // [2, 3, 4]

function isEven(num) {
    return num % 2 === 0;
}

//filter creates a new array with the
//values for which the filter function
//returns a truthy value
arr.filter(isEven) // [2]

function add(a, b) {
    return a + b;
}

//reduce iterates over an array and combines
//the values down into a single value
arr.reduce(add, 0) // 6