console.log(typeof null);      //object
console.log(typeof []);       //object
console.log(typeof {});       //object
console.log(typeof new Date());   //object
console.log(typeof new Object);   //object
console.log(typeof function(){});  //function
console.log(typeof alert);      //function
console.log(typeof 1);        //number
console.log(typeof "abc");      //string
console.log(typeof true);      //boolean

{}.toString.call(obj);

console.log({}.toString.call(null));      //[object Null]
console.log({}.toString.call([]));       //[object Array]
console.log({}.toString.call({}));       //[object Object]
console.log({}.toString.call(new Date()));   //[object Date]
console.log({}.toString.call(function(){}));  //[object Function]
console.log({}.toString.call(new Object));   //[object Object]
console.log({}.toString.call(alert));      //[object Function]
console.log({}.toString.call(1));        //[object Number]
console.log({}.toString.call('abc'));      //[object String]
console.log({}.toString.call(true));      //[object Boolean]

console.log($.type(null));         //null
console.log($.type([]));          //array
console.log($.type({}));          //object
console.log($.type(1));           //number
......不全写完了，结果和{}.toString.call(obj);是一样的