Learn how to create asynchronous programs with JavaScript

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Asynchronous programming is a must in software development. It’s hard to believe that this concept of programming has only been around since the 21st century. The F# programming language was the first among its peers to introduce asynchronous programming, back in 2007.

Other languages ​​such as C#, Python, JavaScript, and C++ gradually added support for asynchronous programming. The big question is: what value does asynchronous programming add to your applications?

This article answers that and other questions, so you’ll learn all about using asynchronous programming.


What is synchronous programming?

Synchronous programming refers to a program in its most basic form. This programming model processes lines of code in a program or script sequentially. It always starts from the first line of code in a program. Then it waits for each line of code to finish executing before moving on to the next one.

The synchronous pattern also includes conditional code, such as if and while statements. Although only part of the code in a conditional statement executes, the program still executes sequentially.

Example of synchronous program

const SyncCode = () => {
console.log("This is the first line in the program")
console.log("This is the second line in the program")
console.log("This is the final line in the program")
}

SyncCode();

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Running the JavaScript program above will produce the following output in the console:

This is the first line in the program
This is the second line in the program
This is the final line in the program

The above output is exactly what you should expect. The program starts at the top and waits for one line of code to complete before moving on to the next.

What is asynchronous programming?

Asynchronous programming is the opposite of synchronous programming. The asynchronous programming model processes multiple lines of code simultaneously. It does not wait for the previous line of code in a program to finish executing before moving on to the next one.

Related: Synchronous vs. Asynchronous Programming: How Are They Different?

Asynchronous programming can cut execution time in half, creating faster computers.

Example of asynchronous program

const AsyncCode = () => {
console.log("This is the first line in the program")
setTimeout(() => {
console.log("This is the second line in the program")
}, 3000)
console.log("This is the final line in the program")
}

AsyncCode();

Running the JavaScript code above will produce the following output in your console:

This is the first line in the program
This is the final line in the program
This is the second line in the program

If you compare the console output above to the asynchronous program that generates it, you will see that there is an obvious difference. The call to Newspaper that says “This is the second line of the program” appears before the one that says “This is the last line of the program”. However, the console output does not reflect this.


Since JavaScript is mostly synchronous, the program code above ran sequentially. But JavaScript supports asynchronous programming through features like setTimeout() method.

the setTimeout() method is an asynchronous JavaScript method that takes two arguments: a function and a delay. Delay is a timer (in milliseconds) that delays execution of the function. So while the above program is waiting for the three seconds to execute the function in the setTimeout() method, it moves to the next line in the code. This results in the execution of the third function call before the second.

Asynchronous JavaScript Technologies

Separated from setTimeout() method mentioned above, several JavaScript technologies use asynchronous programming. These technologies use the asynchronous programming model to develop faster non-blocking applications. Some of these technologies include:


Related: What is Node.js? Here’s how to use server-side JavaScript

Creating asynchronous programs with JavaScript

There are several ways to handle asynchronous code. The method you choose should depend on the type of application you want to develop. These methods include callbacks, promises, and async/await.

Callback functions

There are two important properties of a callback function. They serve as parameters for other functions and they rely on external events to accomplish their duty. the setTimeout() The method used in the asynchronous example above is a callback function. The program passes it a logging function as a parameter (the callback function) and only executes it after three seconds (the event).

Callback functions are great for small programs, but as your applications grow, they can get too complicated very quickly. This is because callback functions often call other callback functions, creating a chain of nested callbacks.

Use promises

JavaScript added support for promises after callback functions. They are a good alternative when creating larger applications. A promise represents what might happen after an asynchronous operation. This potential outcome will take one of two forms: resolved Where rejected. A separate function handles each of these results, removing the need for nesting (the callback function problem). Instead, promises encourage string functions which are easier to use.

Every promise begins with a new To promise object that has an anonymous function with the to resolve and to reject settings. In this function you will have the asynchronous application, which returns a resolution if the asynchronous operation succeeds, or a reject if not.

the then() the string function handles the to resolve function, and the to grab() the string function handles the to reject a function. Thus, there is no need for nested if statements, as is the case with callback functions.

Example of using promises

const PromiseFunction = () =>{
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve("this asynchronous operation executed well")
}, 3000)
})
}

PromiseFunction().then((result) => {
console.log("Success", result)
}).catch((error) => {
console.log("Error", error)
})

The above code returns the following result in the console:

Success this asynchronous operation executed well

This is because the promise returns the to resolve function, which passes its results to the then() a function. If the promise returns the to reject function the program uses the to grab function instead.

Using Async/Wait

If you don’t want to create a chain of promises when dealing with asynchronous operations, you can try async/await. Async/await isn’t a completely different asynchronous tool than promises, just a different way of handling them. It handles promises without using the string method. So, in the same way that promises handle asynchronous operations better than callback functions, async/wait has advantages over simple promises.

There are two key attributes of every async/await function. They start with the asynchronous keyword, and the expect keyword awaits the result of an asynchronous operation.

Sample asynchronous/pending program

const PromiseFunction = () =>{
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve("this asynchronous operation executed well")
}, 3000)
})
}

const AsyncAwaitFunc = async () => {
const result = await PromiseFunction();
console.log(result);
}

AsyncAwaitFunc();

The code above will return the following output to the console:

this asynchronous operation executed well

What are the main takeaways?

There are several major points you should take away from this article:

  • Asynchronous programming is valuable because it reduces the wait time for a program, creating faster applications.
  • A callback function can be synchronous or asynchronous.
  • Promises offer a better way to handle asynchronous operations than callback functions.
  • The async/await functions handle promises better than using the string functions.
  • An async/await function handles asynchronous operations in a way that looks synchronous, which makes it easier to understand.
  • Arrow functions help you write better code.


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