holyfills/lib/array/array_reduce.js

No more "Holy Sxxt!!" when writting ES5/ES6

"use strict";
var assignProperty = require("../helpers/assignProperty");
var ArrayPrototype = require("../helpers/ArrayPrototype");
var toObject = require("../helpers/toObject");
var arrayCanSplitString = require("../helpers/arrayCanSplitString");
var isString = require("../helpers/isString");
var toUint32 = require("../helpers/toUint32");
var isFunction = require("../helpers/isFunction");

module.exports = HAS_ARRAY_REDUCE ? ArrayPrototype.reduce : function (fun /*, initial*/) {
  var object = toObject(this),
      self = arrayCanSplitString && isString(this) ? this.split("") : object,
      length = toUint32(self.length),
      i = 0,
      result;

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

  // 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");
  }

  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, object);
    }
  }

  return result;
};

// 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

assignProperty(ArrayPrototype, "reduce", module.exports, !IS_ARRAY_REDUCE_WORKS_AS_EXPECTED);