JS Judging Object Type

1.typeof

TypeOf can only judge the basic types, number, String, Boolean, Undefined, and object,function;

typeof0;//Number ;typeof true;//Boolean;typeofUndefined//undefined;typeof"Hello World"//string;typeof function(){};//function;typeof NULL;//Objecttypeof{};//object;typeof[];//Object

As we can see from the above example, the TypeOf object and array all return object, so it cannot distinguish between objects and arrays.

2.instanceof

var a=instanceof Object  //truea intanceof Array     // false var b=instanceof Array  //trueinstanceof  //true

Because the array belongs to one of the objects, the array instanceof object, which is also true.

var c= ' abc 'instanceof//falsevar d=new  instanceof String  //true

Instanceof cannot distinguish between the base type string and the Boolean, unless it is a string object and a Boolean object. As shown in the example above.

3.constructor

var o={};o.constructor==object  //truevar arr=[]; Arr.constructor==array  //true//false

You can see that constructor can distinguish between array and object.

var n=true; n.constructor==boolean  //truevar num=1; Num.constructor==number  //truevar str= ' Hello World '; str.constructor ==string     //True

var num=new number ();

Num.constructor==number//true

Note, however, that the constructor property can be modified, causing incorrect results to be detected

function Person () {  }function  Student () {  new person (); var New Student (); Console.log (John.constructor//  false//  true

In addition to undefined and null, other types of variables can use constructor to determine the type. 4.object.prototype.tostring.call ()---------most useful

Object.prototype.toString.call (123)//"[Object number]"  Object.prototype.toString.call (' str ')//"[Object String]"  Object.prototype.toString.call (true)//"[Object Boolean]"  Object.prototype.toString.call ({})//"[Object Object]"  Object.prototype.toString.call ([])//"[Object Array]"

Encapsulates a method for judging arrays and objects

function typeobj (obj) {      var type=Object.prototype.toString.call (obj);       if (type== ' [object array] ') {        return ' array ';      } ElseIf (Type= = ' [Object  object] ')        {return ' object ';      } Else {        return ' obj is not object or array '}      }

When the Object.prototype.toString method is called, the following steps are performed:

1. Gets the class name (object type) of the object.

[[Class]] is an intrinsic property, and all objects (native and host objects) have that property. In the specification, [[class]] is defined as:
Internal property, [[Class]] A string value that indicates the type of the object.
2. Then combine [the name of the object type obtained by] into a string
3. Returns the string "[Object Array]".

$.type interface in 5.jQuery

$.type (obj);

$.isarray (obj);

$.isfunction (obj);

$.isplainobject (obj);

$.type ([])    //array//true$.isfunction (function//  True//true//false

JS Judging Object Type