Programming for beginners: JavaScript: instanceof : Check the class

Thursday, 30 August 2018

JavaScript: instanceof : Check the class

‘instanceof’ operator is used to tests whether an object has in its prototype chain the prototype property of a constructor.

Syntax

object instanceof constructor

instanceof.html

<!DOCTYPE html>

<html>

<head>
    <title>instanceof operator Example</title>
</head>

<body>
    <script>
        function A() {

        }

        function B() {

        }

        function C() {

        }

        // Apply prototype inheritance
        C.prototype = new B();

        var obj = new C(); // obj is instance for both B and C

        document.write("(obj instanceof A) : " + (obj instanceof A) + "<br />");
        document.write("(obj instanceof B) : " + (obj instanceof B) + "<br />");
        document.write("(obj instanceof C) : " + (obj instanceof C) + "<br />");
    </script>
</body>

</html>

Load above page in browser, you can able to see following text.

(obj instanceof A) : false

(obj instanceof B) : true

(obj instanceof C) : true

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Programming for beginners

Thursday, 30 August 2018

JavaScript: instanceof : Check the class

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