JavaScript in operator - GeeksforGeeks

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>
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
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
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