Determination of the type commonly used in four ways

　　1.typeof

　　　　Can correctly determine the primitive types other than null (object type determines a bit touching a)

　　　　Null judgment to be wrong:

　　2.instanceof

　　　　a instanceof b

　　　　It can more accurately determine the type of object, but can not determine the original type

　　　　Principle: Find the b in a prototype chain of whether

　　　　

　　3.constructor (by determining if an instance of a constructor)

 

　　4.toString (recommended Object.prototype.toString.call (), because toString method may be overridden, can not achieve the best results)