array.reduce.polyfill.js

const reduce = function(callback) {
    'use strict';
    if (this == null) {
        throw new TypeError('Array.prototype.reduce called on null or undefined');
    }
    
    if (typeof callback !== 'function') {
        throw new TypeError(callback + ' is not a function');
    }
    
    var t = Object(this),
        len = t.length >>> 0,
        k = 0,
        value;
        
    if (arguments.length == 2) {
        value = arguments[1];
    } else {
        while (k < len && !(k in t)) {
            k++;
        }
        if (k >= len) {
            throw new TypeError('Reduce of empty array with no initial value');
        }
        value = t[k++];
    }
    for (; k < len; k++) {
        if (k in t) {
            value = callback(value, t[k], k, t);
        }
    }
    return value;
};

if (!Array.prototype.reduce) Array.prototype.reduce = reduce;
if (!Float32Array.prototype.reduce) Float32Array.prototype.reduce = reduce;