JavaScript In Operator (2025) -

The in operator is a built-in operator in JavaScript, used to check whether a specific property exists in an object. It returns Boolean true if the specified property is in an object, otherwise it returns false.

Syntax:

prop in object

Parameters: This function accepts the following parameter as shown above and described in detail below:

prop: This parameter holds the string that represents a property name or array index.
object: This parameter is an Object which is to be checked whether it contains the prop.

Return value: This method returns a boolean value:

true: The value true is returned if the specified property is found in an object.
false: The value false is returned if the specified property is not found in an object.

Example 1: Below is an example of the in-operator.

JavaScript

<script> 
    function test() { 
    // Illustration of in operator 
    const array = ['Codes', 'for', 
                'Config'] 
     
    // Output of the indexed number 
    console.log(0 in array); 
     
    // Output of the Value 
    console.log('for' in array); 
     
    // output of the Array property 
    console.log('length' in array); 
    } 
    test(); 
</script>

Output:

true
false
true

Example 2: This example shows the use of the in operator in JavaScript.

JavaScript

<script> 
    // Illustration of in operator 
    const array = ['CodeConfig', 'CodeConfig.in', 
                'Codes', 'Codes1'] 
     
    // Output of the indexed number 
    console.log(0 in array)         
    console.log(2 in array)     
    console.log(5 in array)     
     
    // Output of the Value 
    console.log('for' in array) 
    console.log('CodeConfig.in' in array) 
     
    // output of the Array property 
    console.log('length' in array) 
</script>

Output:

true
true
false
false
false
true

Example 3: Let’s check the use of the in operator with the help of example in JavaScript.

JavaScript

<script> 
    // Illustration of in operator 
    const object = { val1: 'CodeConfig.in', 
                    val2: 'JavaScript', 
                    val3: 'operator', 
                    val4: 'in'}; 
     
    console.log('val1' in object); 
     
    delete object.val1; 
    console.log('val1' in object); 
     
    if ('val1' in object === false) { 
    object.val1 = 'CodeConfig.in'; 
    } 
     
    console.log(object.val1); 
</script>

Output:

true
false
"CodeConfig.in"

Supported Browsers: The browsers supported by JavaScript in operator are listed below:

Google Chrome
Firefox
Opera
Safari
Edge
Internet Explorer

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