Object.assign() polyfill

object.assign.js

if (!Object.assign) {
  Object.defineProperty(Object, 'assign', {
    enumerable: false,
    configurable: true,
    writable: true,
    value: function (target) {
      'use strict';
      if (target === undefined || target === null) {
        throw new TypeError('Cannot convert first argument to object');
      }
      var next, keys, len, key, desc, i, j;
      target = Object(target);
      
      for (i = 1; i < arguments.length; i++) {
        next = arguments[i];
        if (next === undefined || next === null) {
          continue;
        }
        next = Object(next);
        keys = Object.keys(next);
        
        for (j = 0, len = keys.length; j < len; j++) {
          key = keys[j];
          desc = Object.getOwnPropertyDescriptor(next, key);
          if (desc !== undefined && desc.enumerable)
            target[key] = next[key];
        }
      }
      return target;
    }
  });
}