instanceof只能用来判断对象和函数，不能用来判断数字和字符串等；
instanceof右边不能是undefined；
valueof检测null，数组，对象都返回object；
具体看代码：
//ECMAScript typeof and instanceof
var obj = {};
var arr = [];
console.log(typeof 1);//'number'
console.log(typeof 'a');//'string'
console.log(typeof arr);//'object'
console.log(typeof obj);//'object'
console.log(typeof true);//'boolean'
console.log(typeof null);//'object'
console.log(typeof undefined);//'undefined'
console.log( 1 instanceof Number);//false
console.log( 'a' instanceof String);//false
console.log( arr instanceof Array);//true
console.log( true instanceof Boolean);//false
console.log( obj instanceof Object);//true
console.log( null instanceof Object);//false
// console.log( undefined instanceof undefined);
