TypeScript in Operator

Rana Hasnain Khan Feb 15, 2024
TypeScript in Operator

This article will introduce the in operator in TypeScript and how we can use it with examples.

TypeScript in Operator

While working with objects and arrays, there are many situations in which we need to check for the object or array properties. For this purpose, JavaScript provides the in operator that can be used to check whether a property exists in a certain object or not.

The syntax of the in operator is shown below.

# typescript
x in thisObject;

If x exists in the object thisObject, this expression will return true. If x does not exist in the object thisObject, this expression will return false.

Now, let’s go through an example in which we will create an object of fruits and use the in operator to check whether mango exists in the array or not, as shown below.

# typescript
let fruits = {
    fruit1: 'Mango',
    fruit2: 'Banana',
    fruit3: 'Apple',

console.log('fruit1' in fruits);
console.log('fruit3' in fruits);


Check Property Existence in an Object Using TypeScript in operator

As we can see from the above example, using the in operator, we can easily check any property from the object. We can also use this operator on an array, but it will only check for the index in an array.

Rana Hasnain Khan avatar Rana Hasnain Khan avatar

Rana is a computer science graduate passionate about helping people to build and diagnose scalable web application problems and problems developers face across the full-stack.


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