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 false if object is not an instance of the specified class, or if object is null.

The following example illustrates the use of the instanceof operator.

function objTest(obj){
   var i, t, s = "";   // Create variables.
   t = new Array();   // Create an array.
   t["Date"] = Date;   // Populate the array.
   t["Object"] = Object;
   t["Array"] = Array;
      for (i in t)
         if (obj instanceof t[i])   // Check class of obj.
            s += "obj is an instance of " + i + "\n";
            s += "obj is not an instance of " + i + "\n";
   return(s);   // Return string.

var obj = new Date();

Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards. See Version Information.

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