Eloquent JS - Higher Order Function snippet.

EJS - HOF - sumOf.js

function forEach (array, action) {
    for(let i = 0, length = array.length; i < length; i++) {
        action(array[i]);
    }
}

function sumOf(array) {
    let sum = 0;
    forEach(array, value => sum += value);
    return sum;
}