async function javascript dec

What is an async function in JavaScript?

An async function is a function in JavaScript that returns a promise. The execution of an async function is non-blocking, meaning that other code can continue to run while the async function is executing. The purpose of an async function is to simplify asynchronous programming in JavaScript.

How to declare an async function in JavaScript?

To declare an async function in JavaScript, you can use the async keyword before the function declaration. Here’s an example:

async function fetchData() {
  // code goes here
}

How to use an async function in JavaScript?

To use an async function in JavaScript, you can use the await keyword before calling the function. Here’s an example:

async function fetchData() {
  // code goes here
}

async function main() {
  const data = await fetchData();
  // do something with the data
}

In this example, the main() function calls the fetchData() function using the await keyword. This means that the main() function will wait for the fetchData() function to complete before continuing.

What is the purpose of the async keyword in JavaScript?

The async keyword in JavaScript is used to indicate that a function returns a promise. This allows the function to be used with the await keyword, which simplifies asynchronous programming by allowing code to wait for a promise to be resolved before continuing.

What is the role of the await keyword in JavaScript?

The await keyword in JavaScript is used to wait for a promise to be resolved before continuing with the execution of the code. When you use the await keyword, you can write asynchronous code that looks like synchronous code, which makes it easier to read and maintain.

Here’s an example:

async function fetchData() {
  const response = await fetch('https://example.com/data');
  const json = await response.json();
  return json;
}

async function main() {
  const data = await fetchData();
  // do something with the data
}

In this example, the fetchData() function uses the await keyword to wait for the promise returned by the fetch() function to be resolved. Once the promise is resolved, the function uses the await keyword again to wait for the JSON data to be parsed. Finally, the function returns the JSON data, which is then used in the main() function.

What is the difference between an async function and a regular function in JavaScript?

The main difference between an async function and a regular function in JavaScript is that an async function returns a promise, while a regular function does not. This allows an async function to be used with the await keyword, which simplifies asynchronous programming by allowing code to wait for a promise to be resolved before continuing. Regular functions are executed synchronously and cannot be used with the await keyword.

How to handle errors in an async function in JavaScript?

To handle errors in an async function in JavaScript, you can use a try-catch block. Here’s an example:

async function fetchData() {
  try {
    const response = await fetch('https://example.com/data');
    const json = await response.json();
    return json;
  } catch (error) {
    console.error(error);
    throw error;
  }
}

async function main() {
  try {
    const data = await fetchData();
    // do something with the data
  } catch (error) {
    console.error(error);
  }
}

In this example, the fetchData() function uses a try-catch block to handle any errors that may occur while fetching and parsing the JSON data. If an error occurs, the function logs the error to the console and re-throws it. The main() function also uses a try-catch block to handle any errors that may occur while calling the fetchData() function.