正好看到Object.prototype.toString()，通過解釋發(fā)現(xiàn)不光是將現(xiàn)有對(duì)象內(nèi)容轉(zhuǎn)為字符串。

If this method is not overridden in a custom object, toString() returns "[object type]", where type is the object type.

大致理解是在沒有被自定義默認(rèn)的情況下，比如僅僅是通過new構(gòu)造，會(huì)返回[object type]

var o = new Object();
o.toString(); // returns [object Object]

于是利用這個(gè)性質(zhì)，被玩慘了:

var toString = Object.prototype.toString;

toString.call(new Date);    // [object Date]
toString.call(new String);  // [object String]
toString.call(Math);        // [object Math]

// Since JavaScript 1.8.5
toString.call(undefined);   // [object Undefined]
toString.call(null);        // [object Null]

參考鏈接
Object.prototype.toString()