instanceof Operator (JavaScript)

Returns a Boolean value that indicates whether or not an object is an instance of a particular class.


result = object instanceof class  


Required. Any variable.

Required. Any object expression.

Required. Any defined object class.


The instanceof operator returns true if object is an instance of class. It returns true if class is present in the object's prototype chain. It returns false if object is not an instance of class, or if object is null.


The following example shows how to use the instanceof operator.

function objTest(obj){  
    var i, t, s = "";  
    t = new Array();  
    t["Date"] = Date;  
    t["Object"] = Object;  
    t["Array"] = Array;  
        for (i in t){  
            if (obj instanceof t[i]) {   
                s += "obj is an instance of " + i + "<br/>";  
            else {  
                s += "obj is not an instance of " + i + "<br/>";  

var obj = new Date();  

// Output:   
// obj is an instance of Date  
// obj is an instance of Object  
// obj is not an instance of Array  


Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards, Internet Explorer 11 standards. Also supported in Store apps (Windows 8 and Windows Phone 8.1). See Version Information.

See Also

Operator Precedence
Operator Summary (JavaScript)