JavaScript in Operator

The in operator is an inbuilt operator in JavaScript which is used to check whether a particular property exists in an object or not. It returns a boolean value 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 mentioned above and described below:

prop: This parameter holds the string or symbol 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 gfg() {
    // Illustration of in operator
    const array = ['geeks', 'for',
                'geeks']
      
    // 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);
    }
    gfg();
</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 = ['geeksforgeeks', 'geeksfor',
                'geeks', 'geeks1']
      
    // 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('geeksforgeeks' in array)
      
    // output of the Array property
    console.log('length' in array)
</script>

Output:

true
true
false
false
false
true

Example 3: This example shows the use of the in operator in Javascript.

Javascript

<script>
    // Illustration of in operator
    const object = { val1: 'Geeksforgeeks',
                    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 = 'GEEKSFORGEEKS';
    }
      
    console.log(object.val1);
</script>