Understanding Async Functions in JavaScript

In JavaScript, an async function is a function that's implicit promise. It's declared using the async keyword before the function keyword. The correct way to declare it is async function() {}.

Async functions enable us to write promise-based asynchronous code as if it were synchronous, but without blocking the execution thread. It operates asynchronously via the event-loop, uses an implicit Promise to return its result.

Practical Example

Here's an example of how one might define an async function in JavaScript:

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

    console.log(data);
}

fetchData();

Here fetchData is an async function. Inside this function, we use the await keyword to wait for the fetch call and the conversion to JSON to happen.

Best Practices & Extra Insights

Async functions can contain an await expression that pauses the execution of the async function and waits for the passed promise's resolution or rejection, and then resumes the async function's execution and returns the resolved value.

Remember, the await keyword can only be used inside an async function.

In addition to its asynchronicity, error handling in async functions is much simpler and more straightforward. Instead of using .catch, you can use ordinary try/catch blocks.

Example:

async function fetchData() {
    try {
        let response = await fetch('https://api.example.com/data');
        let data = await response.json();

        console.log(data);
    } catch (error) {
        console.error('Error:', error);
    }
}

fetchData();

In this example, if anything goes wrong within the try block (fetch call fails, the response data can't be parsed into JSON, etc.), control goes immediately to the catch block, allowing the error to be dealt with in a neat and understandable manner.

In conclusion, async/await improves the readability and reliability of your asynchronous code, making it appear more like synchronous code.