JavaScript in operator

Last Updated : 11 Sep, 2020

Below is the example of the in operator.

Example 1:

<script> 
    function gfg() { 
    // Illustration of in operator
    const array = ['geeks', 'for', 
                   'geeks']
   
    // Output of the indexed number
    document.write(0 in array);  
      
    // Output of the Value
    document.write('for' in array);
   
    // output of the Array property
    document.write('length' in array);
    } 
    gfg(); 
</script>

Output:
```
true
false
true
```

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 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 to be checked whether it contains the prop.

Return value: This method returns an boolean values :

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.

Below examples illustrate the in operator in JavaScript:

Example 1:

<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 2:

<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>

Output:

> true
> false
> "GEEKSFORGEEKS"

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

Google Chrome
Firefox
Opera
Safari
Edge
Internet Explorer

My Personal Notes

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