在原生不支持的旧环境中添加兼容的Object.keys实现

if (!Object.keys) {
 Object.keys = (function () {
  var hasOwnProperty = Object.prototype.hasOwnProperty, //原型上的方法，只取自身有的属性；
    hasDontEnumBug = !({toString: null}).propertyIsEnumerable('toString'), //ie6一下，！之后的内容为false;
    dontEnums = [
     'toString',
     'toLocaleString',
     'valueOf',
     'hasOwnProperty',
     'isPrototypeOf',
     'propertyIsEnumerable',
     'constructor'
    ],
    dontEnumsLength = dontEnums.length;

  return function (obj) {
   if (typeof obj !== 'object' && typeof obj !== 'function' || obj === null) throw new TypeError('Object.keys called on non-object');

   var result = [];

   for (var prop in obj) {
    if (hasOwnProperty.call(obj, prop)) result.push(prop);
   }

   if (hasDontEnumBug) {
    for (var i=0; i < dontEnumsLength; i++) {
     if (hasOwnProperty.call(obj, dontEnums[i])) result.push(dontEnums[i]);
    }
   }
   return result;
  }
 })()
};