JavaScript in Operator

JavaScript in operator is an inbuilt operator 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:

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

Return value:

This method returns a boolean value. The value true is returned if the specified property is found in an object, else it returns false.

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

Javascript

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();

Output

true
false
true

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

Javascript

// 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)

Output

true
true
false
false
false
true

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

Javascript

// 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);

Output

true
false
GEEKSFORGEEKS

Supported Browsers:

• Google Chrome
• Firefox
• Opera
• Safari
• Edge
• Internet Explorer

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