Imagine juggling a feast of 100 distinct tasks, each like a different delectable dish. Yet, in the midst of this flavorful frenzy, you're inevitably called to partake in the banquet of lunch or the gala of dinner. Alas, the tasks, akin to a sumptuous spread, must momentarily rest on the table of progress—a delicate dance between savoring sustenance and conquering challenges.
Javascript is single-threaded, which means that only one line of code can be executed at a time.
This can be beneficial for performance, as it allows for more efficient use of resources, but it can also be a limitation when dealing with complex tasks that require multiple threads of execution.
If you know what "single-threaded" means, you'll probably relate it to synchronous operations.
In this tutorial, we'll go over the synchronous and asynchronous components of JavaScript. You almost always utilize both in web programming.
Synchronous Vs Asynchronous
In JavaScript, there are two different approaches to handling tasks: synchronous programming and asynchronous programming.
When a program runs synchronously, it completes each task in a linear fashion.
Programming that allows the simultaneous execution of many tasks is known as asynchronous programming.
Tasks can be started and finished out of sequence with asynchronous programming, making better use of the available resources.
With asynchronous programming, you will still be able to be responsive to other events while that task runs, rather than having to wait until that task has finished.
Asynchronous programming is a technique that allows your program to start a task that could take a while to complete and then respond to other events while the task is running, rather than waiting until it is complete.
The asynchronous function has the advantage of providing a fluid user experience.
For instance, if the browser didn't support the asynchronous function, we had to wait until the post comment or follow user operation was complete before we could follow a user on Twitter.
JavaScript, on the other hand, is single-threaded and uses a synchronous execution model.
Synchronous Javascript Programming
One line of synchronous JavaScript code is executed at a time, in the order in which it was written.
This means that before the next line of code can be executed, each line must be finished.
Synchronous JavaScript is the most popular JavaScript code for online applications.
When it's important to make sure a task is finished before moving on to the next, synchronized JavaScript is utilized.
Code execution is essential to ensuring data is processed in the proper sequence.
Synchronous JavaScript can also be used for debugging and troubleshooting, which is useful for ensuring predictable code execution.
The following are some situations where synchronous Javascript is useful:
Ajax queries, which enable data to be obtained from a server without reloading the page, can be made using synchronized JavaScript.
Events can be handled using synchronized JavaScript, including mouse clicks, keystrokes, and form submissions.
Synchronous JavaScript: The Hidden Facts
When a synchronous JavaScript application is run, the JavaScript engine creates a call stack to keep track of the order in which functions are invoked.
The call stack is a data structure that stores information about active functions.
When a function is invoked, it moves to the top of the call stack.
The JavaScript engine keeps track of the current line of code being performed as the function proceeds. When the function returns, it is removed from the call.
In a synchronous JavaScript program, a call stack is a data structure that keeps track of the order in which functions are called.
It is a Last In First Out (LIFO) data structure, which means that the most recently called function is the first to be popped off the stack.
Synchronous JavaScript refers to the execution of JavaScript code in a sequential manner, where each line of code is executed one after the other.
This means that if one line of code takes a long time to execute, then all subsequent lines of code will have to wait until that line of code is executed before they can be executed.
Here's an example of synchronous JavaScript code:
function addNumbers(x, y) {
console.log("Start function");
let result = x + y;
console.log("End function");
return result;
}
console.log("Before function");
let sum = addNumbers(3, 4);
console.log("After function");
console.log(sum);
In the code above, we have a function called addNumbers that takes in two arguments x and y and returns their sum. The function also logs a message to the console before and after the computation.
Next, we have some code outside of the function that logs a message to the console before and after calling the function, and then logs the result of the function.
When this code is executed, the following output will be printed to the console:
Before function
Start function
End function
After function
7
As you can see, the code is executed in a sequential manner. The console.log statement before the function is executed first, then the function is executed, followed by the console.log statement after the function, and finally, the result of the function is printed to the console.
The problems with synchronous programming
One important thing to note is that synchronous JavaScript can sometimes result in the browser or the application becoming unresponsive if a long-running operation is executed.
This is because synchronous JavaScript blocks the main thread of execution, which is responsible for handling user interactions and rendering the UI. To avoid this, we can use asynchronous JavaScript, which allows for non-blocking execution of code.
Synchronous Javascript development has a few disadvantages, including the potential for challenges with scaling, maintenance, and debugging.
Furthermore, because synchronous programming necessitates extensive manual testing, it might be challenging to test.
Synchronous programming requires coordination between components, making it difficult to implement.
Be aware that asynchronous programming is not the answer to synchronous programming.
There are several programming issues that asynchronous programming can help with, but it does not address all of them.
Synchronized programming is necessary for some activities, such as waiting for a response from a server before continuing.
Asynchronous Javascript
You've undoubtedly heard the phrase "asynchronous" before if you've been studying JavaScript for a while.
Do note that Javascript is a synchronous language, with asynchronous capabilities.
Programming in JavaScript that is asynchronous enables numerous processes to be carried out concurrently without interrupting the main thread.
It is a style of coding that permits non-blocking activities, which means that the program can keep running while waiting for a job to finish.
Asynchronous programming, which is commonly used to improve performance, allows web applications to do multiple tasks at the same time.
Why asynchronous Approach?
JavaScript is single-threaded and has a global execution context, as we learned earlier.
As a result, by design, JavaScript is synchronous and has a single call stack. Code will be executed in the last-in, first-out (LIFO) order in which it is called.
Asynchronous programming is vital because it allows multiple processes to run concurrently without interfering with the main thread.
This is significant because the main thread is in charge of managing the call stack, which is a data structure that holds the current sequence of function calls.
Blockage of the main thread leads to decreased performance. Because async programming permits the main thread to stay unblocked, additional tasks can be completed while the asynchronous task is ongoing.
To explain this, let’s look at the code below:
console.log("asynchronous.");
setTimeout(() => console.log("asynchronous javascript!"), 3000);
console.log("asynchronous again!");
The code above won't run synchronously on the JavaScript engine, in contrast to our prior example.
Let's look at the output displayed below:
// asynchronous.
// asynchronous again!
// asynchronous javascript!
Step 1: The first line of code will be executed, logging the string "asynchronous" to the console.
Step 2: The setTimeout method is invoked, which will execute the anonymous function after 3 seconds (3000 miliseconds). The anonymous function will log "asynchronous javascript!" to the console.
Step 3: The third line of code will be executed, logging the string "asynchronous again!" to the console.
Step 4: After 3 seconds, the anonymous function from the setTimeout method will be executed, logging "asynchronous javascript!" to the console.
In other words, with asynchronous JavaScript, the JavaScript doesn't wait for answers before continuing to execute subsequent functions.
This is useful for applications that require a lot of processing power since it permits numerous tasks to be completed at the same time.
Techniques for writing asynchronous JavaScript
There are several techniques that allow JavaScript to run asynchronously.
By using these asynchronous techniques, we can make JavaScript more efficient and responsive, allowing for the creation of complex applications that can handle multiple tasks simultaneously without affecting the user experience.
We will discuss
Callbacks
Promises
Async/await
Callbacks: This allows for asynchronous code to be written in a synchronous fashion.
Employ promises: writing asynchronous JavaScript code is made easy with promises.
They enable you to create code that runs after a predetermined period of time or when a predetermined condition is satisfied.
Utilize Async/Await: Async/Await is a more recent technique for creating asynchronous JavaScript code.
It helps you write more succinct and readable code that will execute after a set period of time or when a set condition is met.
Callbacks
A callback is a function that executes after the outer code call has finished running. It is supplied as an input to another function.
When a function has completed its purpose, it is utilized to enable it to invoke another function.
In order to carry out asynchronous actions in JavaScript, such as executing an AJAX request or anticipating a user click, callbacks are widely utilized.
After the asynchronous operation is complete, the callback function is invoked with the operation's result.
function doSomething(callback) {
setTimeout(function () {
// do something
callback();
}, 1000);
}
function doSomethingElse(callback) {
setTimeout(function () {
// do something else
callback();
}, 1000);
}
function doThirdThing(callback) {
setTimeout(function () {
// do third thing
callback();
}, 1000);
}
This code is an example of asynchronous programming. The doSomething(), doSomethingElse(), and doThirdThing() functions all take a callback as an argument.
When the functions are invoked, they first run the code contained in the setTimeout() method before executing the callback function that was supplied.
The code above demonstrates an example of using callback functions in JavaScript. However, when multiple callbacks are used in succession, it can lead to a problem known as callback hell.
Callback hell occurs when the code becomes difficult to read and manage due to the number of nested callbacks that are required to handle asynchronous operations.
In the example code above, if we wanted to execute doSomething, doSomethingElse, and doThirdThing in sequence, we would need to nest the callbacks as follows:
doSomething(function() {
doSomethingElse(function() {
doThirdThing(function() {
// do something after all three functions complete
});
});
});
As more functions are added to the sequence, the nesting becomes deeper and the code becomes more difficult to read and manage.
This can lead to bugs and errors, as it becomes difficult to keep track of the flow of data and control in the code.
To avoid callback hell, developers can use alternative techniques such as promises and async/await.
Promise
An async promise operation's eventual success or failure is represented as a JavaScript object.
It enables the creation of asynchronous code that works and appears synchronous.
There are three possible states for a promise: pending, fulfilled, or rejected.
A promise is unfulfilled when an asynchronous operation is still in progress.
Promise fulfillment indicates the successful completion of an asynchronous operation.
Rejecting a promise indicates that an asynchronous operation has failed.
// Example using promises
const getValue = () => {
return someAsyncOperation().then((value) => {
return value;
});
};
Promises are used in this code to carry out an asynchronous operation.
The someAsyncOperation() function is used by the getValue() function to perform an asynchronous operation, and the operation's result is then returned.
To manage the promise and return the result of the asynchronous operation, use the.then() method.
Async/await
Async/await is a technique for building asynchronous code that looks and behaves like synchronous code.
The async keyword is used to define an asynchronous function. When a function is marked as async, it always returns a Promise that resolves with the value returned by the function.
Within an async function, we can use the await keyword to pause the execution of the function until a Promise is resolved.
It enables you to construct code that appears to run in sequence but operates asynchronously.
This function simplifies the reading and writing of code that employs asynchronous operations.
// Example using async/await
const getValue = async () => {
const value = await someAsyncOperation();
return value;
};
To conduct an asynchronous operation, this code employs the async/await idiom.
The async method getValue is declared, which means it will return a Promise.
Before continuing, the await keyword is used within the method to wait for the result of the asynchronous action someAsyncOperation().
When the action is finished, the function returns the value.
Conclusion
In this post, we explored the differences between synchronous and asynchronous JavaScript.
We examined the synchronous JavaScript call stack's internal workings, and learned how to build asynchronous JavaScript using promises and async/await.
We have seen that callbacks are simple functions passed to other functions and are only executed when an event is completed.
Additionally, we have also seen that async operations can run concurrently without disturbing the main thread.
For further study, here are some resources on asynchronous JavaScript.