TS Promises

What are Promises?

Promises in JavaScript provide a way to handle asynchronous operations. They represent a value that may be available now, or in the future, or never. Promises can be in one of three states: pending, fulfilled, or rejected.

TypeScript enhances promises by allowing you to define the type of the resolved value, offering better type safety and development experience.

Creating a Promise in TypeScript

Creating a promise in TypeScript is similar to JavaScript. However, you can specify the type of data the promise will resolve to, enhancing the reliability and readability of your code.

Here's a basic example of a promise that resolves to a number:

Using Generic Types with Promises

TypeScript's use of generic types with promises allows you to specify not just that a promise will resolve, but what it will resolve to. This feature is particularly useful in functions that return promises:

Consider a function that fetches a user's data from an API and returns a promise:

Handling Promise Rejection

Handling rejected promises is crucial for robust applications. You can use the catch method to handle errors or rejections. Here’s how you can handle a rejected promise:

Chaining Promises

Promises can be chained to perform a sequence of asynchronous operations. Each call to then returns a new promise, so you can chain them to create a series of asynchronous tasks:

Summary

TypeScript promises are a powerful tool for managing asynchronous operations with the added benefit of type safety. By leveraging generic types, you can ensure that your code is reliable and understandable, making it easier to maintain and less prone to errors.

In this post, we've covered the basics of creating, using, and handling promises in TypeScript. Next, we'll explore how promises are utilized with the Fetch API to make HTTP requests efficiently.