Understanding the 'async' Keyword in JavaScript

Using the async keyword in JavaScript plays a significant role in handling asynchronous operations in your code. Its primary purpose is to declare a function as asynchronous, transforming it into an AsyncFunction object.

What does 'async' do in JavaScript?

The 'async' keyword enables you to write promise-based asynchronous code in a more synchronous, or cleaner, manner. When a function is declared with the async keyword, it automatically returns a promise.

The full syntax looks something like this:

async function myFunction() {
   // code
}

In this syntax, myFunction is declared as an asynchronous function. If this function returns a value, the promise will be resolved with the returned value. However, if the function throws an exception, the promise is rejected with the thrown error.

Practical Applications of 'async'

One of the main reasons to use 'async' is to use the 'await' keyword inside the function. The 'await' keyword can pause the execution of the function until a promise is resolved or rejected. This makes asynchronous code appear synchronous and easier to read and write.

Here's a quick example to showcase this:

async function fetchUser() {
  let response = await fetch('https://api.example.com/user');
  let data = await response.json();
  console.log(data);
}

In the above code, the 'await' keyword is used to pause the execution of the fetchUser function until the fetch function resolves to a value. The code after the 'await' keyword doesn't run until a promise settles, making asynchronous code look like it's synchronous.

Best Practices

While working with 'async' keyword, here are a few best practices to follow:

• Although 'async' functions make it seem as if the asynchronous task is happening synchronously, one should be mindful that the real nature of the task is still asynchronous.
• You should handle promise rejections using try/catch blocks.
• Make sure not to overuse 'async/await'. Not everything needs to be awaited. In some cases, Promises and callbacks may serve you better and keep your code cleaner.

In conclusion, the 'async' keyword in JavaScript is utilized to declare a function as asynchronous, enabling us to write cleaner and more readable asynchronous code.