4.Object.prototype.toString.call()
1 var a = Object.prototype.toString; 2 3 console.log(a.call("aaa")); 4 console.log(a.call(1)); 5 console.log(a.call(true)); 6 console.log(a.call(null)); 7 console.log(a.call(undefined)); 8 console.log(a.call([])); 9 console.log(a.call(function() {})); 10 console.log(a.call({}));