How to use the "in" operator in TypeScript

In TypeScript, the in operator is used to check if a property exists in an object or if an index exists in an array. Here's how you can use it:

Checking for a property in an object:

typescriptCopy code
interface MyObject {
  name: string;
  age: number;
}

const myObject: MyObject = {
  name: 'John',
  age: 25,
};

if ('name' in myObject) {
  console.log('Property "name" exists in myObject.');
} else {
  console.log('Property "name" does not exist in myObject.');
}

Checking for an index in an array:

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const myArray: string[] = ['apple', 'banana', 'orange'];

if (1 in myArray) {
  console.log('Index 1 exists in myArray.');
} else {
  console.log('Index 1 does not exist in myArray.');
}

In the array example, the in operator checks if the index 1 exists in the array myArray. If the index exists, it will execute the code inside the if block; otherwise, it will execute the code inside the else block.

Using the in operator is a type-safe way to check for the existence of properties or indices, and TypeScript will provide appropriate type checking and autocompletion based on the type of the object or array.