typeof(number,string,undefined,boolean,object)
会出现以上5种情况中的一种
console.log(typeof('123'));//stringconsole.log(typeof(123));.//numberconsole.log(typeof(10.1));//numberconsole.log(typeof(NaN));//numberconsole.log(typeof(undefined));//undefinedconsole.log(typeof(true));//booleanconsole.log(typeof([1,2,3]));//objectconsole.log(typeof({ 'username':'user1', 'say':function(){alert('hello')}}));//objectconsole.log(typeof(document));//objectconsole.log(typeof(newObject()));//objectconsole.log(typeof(null));//object