Asynchronous programming is an important topic in TypeScript because it allows you to write code that doesn’t block the main thread. This is essential for building scalable and responsive applications. In this section, we’ll cover how to work with asynchronous code in TypeScript.

Callbacks

The simplest way to work with asynchronous code in TypeScript is through callbacks. A callback is a function that is passed as an argument to another function, which is called when the asynchronous operation is complete. Here’s an example:

function fetchData(callback: (data: string) => void) {
  setTimeout(() => {
    callback("Some data");
  }, 1000);
}

fetchData((data) => {
  console.log(data);
});

In this example, the fetchData function takes a callback function as its argument. It then waits for 1 second using the setTimeout function, and then calls the callback function with some data. When we call fetchData, we pass in an anonymous function that logs the data to the console.

Promises

While callbacks are a simple way to work with asynchronous code, they can quickly become unwieldy when you have to chain multiple operations together. Promises provide a more structured way to work with asynchronous code.

A Promise is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. Here’s an example of how to use Promises in TypeScript:

function fetchData(): Promise<string> {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve("Some data");
    }, 1000);
  });
}

fetchData()
  .then((data) => {
    console.log(data);
  })
  .catch((error) => {
    console.error(error);
  });

In this example, the fetchData function returns a Promise that resolves with some data after 1 second. We then use the then method to handle the resolved value, and the catch method to handle any errors that might occur.

Async/await

Async/await is a more recent addition to TypeScript and provides a way to write asynchronous code that looks like synchronous code. It’s built on top of Promises and makes it easier to work with them.

Here’s an example of how to use Async/await in TypeScript:

async function fetchData(): Promise<string> {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve("Some data");
    }, 1000);
  });
}

async function main() {
  try {
    const data = await fetchData();
    console.log(data);
  } catch (error) {
    console.error(error);
  }
}

main();

In this example, we define an async function called fetchData that returns a Promise. We then define another async function called main that uses await to wait for the Promise to resolve. We handle errors with a try/catch block.

Conclusion

Asynchronous programming is a fundamental aspect of building modern applications, and TypeScript provides several tools to help you work with it. Callbacks, Promises, and Async/await are all important techniques to be familiar with. By using these tools, you can write scalable and responsive code that takes full advantage of the power of TypeScript.