Object.assign(): オブジェクトをシャローコピー(ES6 Polyfill)

es6-object-assign.js

/**
 * es6-object-assign.js
 *
 * Object.assign( target, ...sources )
 * The assign function is used to copy the values of all of the enumerable own properties from one or more source objects to a target object. When the assign function is called, the following steps are taken. (ECMA-262 6th Edition / ECMAScript 2015)
 *
 * @version 1.0.0
 * @author think49
 * @url https://gist.github.com/think49/a615978e85f44cb0ef5c7cbdd3cca942
 * @license http://www.opensource.org/licenses/mit-license.php (The MIT License)
 * @see <a href="http://www.ecma-international.org/ecma-262/8.0/#sec-object.assign">19.1.2.1O bject.assign ( target, ...sources ) - ECMAScript® 2017 Language Specification</a>
 */

'use strict';
if (typeof Object.assign !== 'function') {
  Object.defineProperty(Object, 'assign', {
    writable: true,
    enumerable: false,
    configurable: true,
    value: (function (Object, keys) {
      return function assign (target, source /* [,... source] */) {
        'use strict';

        if (typeof target === 'undefined' || target === null) {
          throw new TypeError('Cannot convert undefined or null to object');
        }

        var len = arguments.length, i = 1;

        target = Object(target);

        while (i < len) {
          source = arguments[i++];

          if (typeof source !== 'undefined' && source !== null) {
            source = Object(source);

            for (var j = 0, sKeys = keys(source), sLen = sKeys.length, key; j < sLen; ++j) {
              key = sKeys[j];
              target[key] = source[key];
            }
          }
        }

        return target;
      };
    }(Object, Object.keys))
  });
}