What is the in operator in JavaScript with Examples?

The in operator helps us to check if a property is in the object. It returns true if a property exists in the object. Otherwise false if the property does not exist.

Here is how you use the in operator in JavaScript.

prop in object

• prop is the property name you want to check if it is present in the object.
• object is the object in which the property can be.

Let's see some examples that show you how to use the in operator in JavaScript.

Example 1: To check if a property exists in an object

let pdt = {
  name: "Coral Straight Fit Kurta",
  price: 1039,
  size: ["S", "M", "L"],
  color: "Coral"
}

console.log('price' in pdt); //true
console.log('size' in pdt); //true

console.log('fabric' in pdt); //false

As you can see, the price property is in the pdt object, so the in operator returns true. On the other hand, the fabric property is not present that is why the in operator returns false.

Using the in operator, you can also check if an inherited property exists in an object or not.

let pdt = {
  name: "Coral Straight Fit Kurta",
  price: 1039,
  size: ["S", "M", "L"],
  color: "Coral"
}

console.log('toString' in pdt); //true

The toString is a method that is inherited from the Object to the pdt object.

Example 2: To check if an index exists in an array

The in operator is also used to check if an index is present in the array.

let arr = [11, 22, 33, 44];
console.log(1 in arr); //true
console.log(3 in arr); //true

console.log(4 in arr); //false

As you can see that the array has index positions from 0 to 3.

4 is not an index position, that is why the in operator returns false.

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