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JavaScript Instanceof Operator - GeeksforGeeks

JavaScript Instanceof Operator

Last Updated : 11 Jul, 2025

The instanceof operator in JavaScript is used to check the type of an object at run time. It returns a boolean value if true then it indicates that the object is an instance of a particular class and if false then it is not. 

Syntax: 
let gfg = objectName instanceof objectType
Parameters:

Return Value: This method returns a boolean value if true then it indicates that the object is an instance of a particular class and if false then it is not. 

Example 1: Below is the example of the Instanceof Operator.

html 
<!DOCTYPE html>
<html lang="en">

<head>
    <title>
        How to Check/Uncheck the
        checkbox using JavaScript ?
    </title>
</head>

<body>
    <h1 style="color:green">
        GeeksforGeeks
    </h1>
    <h3>
        Instanceof Operator.
    </h3>

    <p id="GFG"></p>

    <script>
        let a = ["Geeks", "for", "Geeks"];

        document.getElementById("GFG").innerHTML =
            (a instanceof Array) + "<br>" +
            (a instanceof Number);
    </script>
</body>

</html>

Output: 

JavaScript Instanceof Operator

 Example 2: Below is the example of the Instanceof Operator.

html 
<!DOCTYPE html>
<html lang="en">

<head>
    <title>
        How to Check/Uncheck the
        checkbox using JavaScript ?
    </title>
</head>

<body>
    <h1 style="color:green">
        GeeksforGeeks
    </h1>
    <h3>
        Instanceof Operator.
    </h3>

    <p id="GFG"></p>

    <script>
        let fruits = ["Apple", "Mango", "Banana"];

        document.getElementById("GFG").innerHTML =
            (fruits instanceof Array) + "<br>" +
            (fruits instanceof Object) + "<br>" +
            (fruits instanceof String) + "<br>" +
            (fruits instanceof Number);
    </script>
</body>

</html>

Output:

JavaScript Instanceof Operator

 Example 3: Demonstrating that String and Date objects are also a type of Object (derived from Object). 

JavaScript 
<script>
    var myString = new String();
    var myDate = new Date();
    
    console.log(myString instanceof Object);
    console.log(myString instanceof Date);
    console.log(myString instanceof String);
    console.log(myDate instanceof Date);
    console.log(myDate instanceof Object);
    console.log(myDate instanceof String);
</script>

Output:

true
false
true
true
true
false

We have a complete list of Javascript Operators, to check those please go through the Javascript Operators Complete Reference article.

Supported Browsers:


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