js类型判断

console.log(typeof "a"); //string
console.log(typeof 1); //number
console.log(typeof true); //boolean
console.log(typeof []); //object
console.log(typeof new {}); //object
console.log(typeof null); //object
var a;
console.log(typeof a); //undefined
console.log(typeof function(){}); //function

var type=Object.prototype.toString;
console.log(type.call("a")); //[object String]
console.log(type.call(1)); //[object Number]
console.log(type.call(true)); //[object Boolean]
console.log(type.call([])); //[object Array]
console.log(type.call({})); //[object Object]
console.log(type.call(null)); //[object Null]
var a;
console.log(type.call(a)); //[object Undefined]
console.log(type.call(function(){})); //[object Function]