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.
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
- 0 in array returns true because index 0 exists in the array.
- 'for' in array returns false because the in operator checks for indexes or property names, not values.
- 'length' in array returns true because length is a built-in property of arrays.
Syntax:
prop in object
Here are some examples of using the in operator:
Example: Using the in Operator to Check Indexes and Properties in an Array.
// 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
- 0 and 2 exist as indexes: true, 5 does not : false.
- 'for' and 'geeksforgeeks' are values, not property names : false.
- 'length' is a built-in array property : true.
Example: Using the in Operator to Check the Existence of Properties in an Object.
// 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
- 'val1' in object returns true because the property exists
- After deleting object.val1, it returns false since the property no longer exists.
- The code checks for the missing property and recreates it with a new value.
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.