"Front End Learning Note 01" javascript Source method for judging data types

primitive Type (value type): Undefined, Null, number, String, Boolean;

Object Type (reference type): Object;

typeof

The standard type can be recognized, null outside (return object), and no specific object type (function excepted) is recognized.

Examples of usage:

var num = 100;typeof num;  

Note: Except for number, String, Boolean, undefined, and function types, the remaining types are judged to be object (including null).

instanceof

You can identify built-in object types, custom object types, and cannot discriminate between primitive types.

var arr = [];arr instanceof Array; -->true

Object.prototype.toString.call ()

You can identify the standard type, built-in object type, and not the custom object type.

Object.prototype.toString.call (123); --[Object number]

Constructor

The built-in object types, custom object types, and standard types can be distinguished (but underfined/null not recognized).

var num = 100;num.constructor = = = number; --true;

Return constructor Syntax:

function Getconstructorname (obj) {    return (obj===undefined| | obj===null)? obj: (obj.constructor&&obj.constructor.tostring (). Match (/function\s* ([^ (]*)/) [1]);} Match () Gets the number in the returned function number () {[native code]}.

"Front End Learning Note 01" javascript Source method for judging data types