How to return values from Javascript async functions using async-await?

Asynchronous programming has become a crucial aspect of contemporary web development, and async functions are a valuable resource for handling intricate code flows. By utilizing async-await, writing asynchronous code that resembles synchronous code has become more effortless, resulting in an improvement in the codebase’s legibility and maintainability. Despite this, returning values from async functions is a frequent challenge for developers working on such tasks. This post outlines how to use JavaScript’s async-await from function to return values from async functions.

Understanding Async Functions:

Async functions are a type of function that allows us to write asynchronous code that appears synchronous. These functions return a promise because they employ the ‘async’ keyword. To make working with asynchronous code easier, the ‘await’ keyword is used to pause the function until the promise is fulfilled. Here’s an instance:

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

In this example, the getData function requests data from a network using the fetch function. The await expression is used to receive a promise returned by the fetch function. By suspending the execution of the getData function until the promise is fulfilled, the await expression facilitates working with asynchronous code. The value that is resolved is then assigned to the response variable.

The json method is then applied to the response variable, which returns a second promise containing the JSON-parsed data. This promise is also passed to an await expression, which again suspends execution of the getData function until the promise is fulfilled.

Finally, the resolved value of the second promise is returned from the getData function, allowing the calling code to access the data that was fetched from the network.

How to return values from async functions using async-await

Returning values from async functions using async-await is a simple process that operates similarly to returning values from synchronous functions. To accomplish this, you use the return statement within the body of the async function, followed by the value you want to return.

Here is a simple example of an async function that returns a string:

async function getMessage() {
return 'Hello, world!';
} 

The Async-Await from Function:

The async-await from function is a shorthand way of writing async functions that return a value. It allows us to write code that looks synchronous, but is actually asynchronous. The syntax is as follows:

const value = await someAsyncFunction();

Using Async-Await from Function to Return Values:

To return values from async functions using async-await from function, we simply need to include the ‘return’ keyword before the function call. For example:

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

async function processData() {
const data = await fetchData();
return data.length;
}

processData().then(length => {
console.log(length); // Output: length of data
}); 

Best Practices for Returning Values from Async Functions:

Always use the ‘return’ keyword to return a value from an async function.
Use descriptive variable names to make the code more readable.
Use error handling to catch and handle any errors that may occur.

In this example, the getMessage function returns the string ‘Hello, world!’. To access the returned value, you can use the await operator in another async function, like this:

async function main() {
let message = await getMessage();
console.log(message);
} 

In this example, the `main` function uses the `await` operator to pause its execution until the `getMessage` function has completed and returned its value. The returned value is then assigned to the `message` variable, which is logged to the console.

It’s important to note that you can only use the `await` operator inside an async function. If you try to use it outside of an async function, you will get a syntax error.

Best practices and common pitfalls

When using async functions and the await operator, there are a few best practices and common pitfalls to keep in mind.

– Always use `try-catch` blocks when using the `await` operator to handle any errors that might occur during the asynchronous operation.

– Use the `async` keyword on functions that perform asynchronous operations, even if they don’t use the `await` operator. This makes it clear to other developers that the function is asynchronous and should be treated as such.

– Avoid using the `await` operator inside loops, as this can result in poor performance. Instead, try to use the `Promise.all` method to perform multiple asynchronous operations in parallel.

### Common pitfalls

– Forgetting to use the `await` operator. If you forget to use the `await` operator, your code will continue to execute asynchronously, which might not be what you want.

– Assuming that an async function returns immediately. Just because an async function is defined using the `async` keyword doesn’t mean that it returns immediately. It’s important to always use the `await` operator or handle the returned promise appropriately.

– Using `await` with non-promises. The `await` operator can only be used with promises. If you try to use it with a non-promise value, you will get an error.

– Blocking the event loop. If you use the `await` operator inside a loop, you run the risk of blocking the event loop and causing your program to hang. To avoid this, try to use the `Promise.all` method to perform multiple asynchronous operations in parallel.

In summary, async functions and the await operator are potent resources for composing asynchronous code in JavaScript. When utilized correctly, they allow you to write asynchronous code that appears and operates like synchronous code, improving its readability and maintainability. However, it is important to keep in mind the best practices and typical issues while utilizing async-await in your own code.