LeetCode/problems/js/array-reduce-transformation.js

/**
 * @param {number[]} nums
 * @param {Function} fn
 * @param {number} init
 * @return {number}
 */
var reduce = function(nums, fn, init) {
    let val = init;

    for (let x of nums) {
        val = fn(val, x);
    }

    return val;
};