raptor-polyfill/array/reduce.js

Polyfills for various EcmaScript 5 and EcmaScript 6 methods distributed as CommonJS modules that can be require'd individually or as a whole.

// ES5 15.4.4.21
// http://es5.github.com/#x15.4.4.21
// https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Objects/Array/reduce
if (!Array.prototype.reduce) {
    var toObject = require('./_toObject');

    Array.prototype.reduce = function reduce(fun /*, initial*/) {
        var self = toObject(this),
            length = self.length >>> 0;

        // If no callback function or if callback is not a callable function
        if (typeof fun !== "function") {
            throw new TypeError();
        }

        // no value to return if no initial value and an empty array
        if (!length && arguments.length == 1) {
            throw new TypeError('reduce of empty array with no initial value');
        }

        var i = 0;
        var result;
        if (arguments.length >= 2) {
            result = arguments[1];
        } else {
            do {
                if (i in self) {
                    result = self[i++];
                    break;
                }

                // if array contains no values, no initial value to return
                if (++i >= length) {
                    throw new TypeError('reduce of empty array with no initial value');
                }
            } while (true);
        }

        for (; i < length; i++) {
            if (i in self) {
                result = fun.call(void 0, result, self[i], i, self);
            }
        }

        return result;
    };
}