How to Write Asynchronous Function in JavaScript?

Summary: In this tutorial, you will learn to write asynchronous function in Javascript using Promises and async/await.

To write an asynchronous function in JavaScript, you can use either Promises or async/await.

Asynchronous Function using Promises

Here is an example of an asynchronous function using Promises:

const myAsyncFunc = () => {
  return new Promise((resolve, reject) => {
    // Do something asynchronous
    setTimeout(() => {
      // If the async operation is successful, call resolve
      resolve('Async operation complete');
    }, 1000);
  });
}

myAsyncFunc().then((result) => {
  console.log(result); // 'Async operation complete'
});

Here, the myAsyncFunc function is an asynchronous function that returns a Promise. A Promise is an object that represents the result of an asynchronous operation.

The myAsyncFunc function uses the setTimeout function to execute some code after a specified amount of time (in this case, one second).

Inside the setTimeout callback, the resolve function is called with the string ‘Async operation complete’ as an argument. This causes the Promise to resolve to the value ‘Async operation complete’.

The myAsyncFunc function is called by the code myAsyncFunc().then((result) => { console.log(result); });.

The then method is called on the returned Promise, and it takes a callback function as an argument. This callback function is executed when the Promise resolves, and it receives the resolved value as an argument (in this case, ‘Async operation complete’).

Asynchronous Function using async/await

Here is an example of an asynchronous function using async/await:

const myAsyncFunc = () => {
  return new Promise((resolve, reject) => {
    // Do something asynchronous
    setTimeout(() => {
      // If the async operation is successful, call resolve
      resolve('Async operation complete');
    }, 1000);
  });
}

async function myAsyncFunction() {
  const result = await myAsyncFunc();
  console.log(result); // 'Async operation complete'
}

myAsyncFunction();

In this example, the myAsyncFunc function is the same as in the first example. The myAsyncFunction function is an asynchronous function that calls myAsyncFunc and waits for the Promise to resolve using the await keyword.

The await keyword can only be used inside an async function, and it causes the code to pause until the Promise is resolved.

In this case, the await keyword is used to wait for the myAsyncFunc Promise to resolve, and then the resolved value is stored in the result variable. Finally, the result variable is logged to the console.