Synchronous VS Asynchronous - Javascript (Simple Examples)
Published: 2022-07-25 04:13:00

## JavaScript is a single-threaded, non-blocking, asynchronous, concurrent programming language with lots of flexibility.

- Javascript is synchronous “by default”. Meaning, the next line of code cannot run until the current one has finished. The next function cannot run until the current one has been completed.

- But when it comes to asynchronous, blocks of code run in parallel, and functions are processed independently.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/0ovpk0gwjblmouru9dg4.png)


## Asynchronous programming
Asynchronous programming, conversely, is a multithreaded model that’s most applicable to networking and communications. Asynchronous is a non-blocking architecture, which means it doesn’t block further execution while one or more operations are in progress.

With asynchronous programming, multiple related operations can run concurrently without waiting for other tasks to complete. During asynchronous communication, parties receive and process messages when it’s convenient or possible to do so, rather than responding immediately upon receipt.

Texting is an asynchronous communication method. One person can send a text message and the recipient can respond at their leisure. In the meantime, the sender may do other things while waiting for a response.

## Synchronous programming
Synchronous is known as a blocking architecture and is ideal for programming reactive systems. As a single-thread model, it follows a strict set of sequences, which means that operations are performed one at a time, in perfect order. While one operation is being performed, other operations’ instructions are blocked. The completion of the first task triggers the next, and so on.

To illustrate how synchronous programming works, think of a telephone. During a phone call, while one person speaks, the other listens. When the first person finishes, the second tends to respond immediately.

## When to use async
Asynchronous programming should only be used in programming independent tasks, where it plays a critical role. For instance, asynchronous programs are ideal for development projects with a large number of iterations. Because steps don’t have to follow a fixed sequence, asynchronous programming keeps development moving forward.

Responsive UI is a great use case for asynchronous planning. Take, for example, a shopping app. When a user pulls up their order, the font size should increase. Instead of first waiting to load the history and update the font size, asynchronous programming can make both actions happen simultaneously.

## When to use sync
Asynchronous programming is relatively complex. It can overcomplicate things and make code difficult to read. Synchronous programming, on the other hand, is fairly straightforward; its code is easier to write and doesn’t require tracking and measuring process flows (as async does). Because tasks are dependent on each other, there’s a need to know if they could run independently without interrupting each other.

Synchronous programming could be appropriate for a shopping app, for example. When checking out online, a user wants to buy all of their items together, not individually. Instead of completing an order every time the user adds something to their cart, synchronous programming ensures that the payment method and shipping destination for all items are selected at the same time.

## How to choose between asynchronous and synchronous programming
When deciding which approach to take, it may be helpful to think of asynchronous programming as adaptable, and synchronous programming as strict. Asynchronous programming is the multitasker, moving from one task to the other and alerting the system when each one is complete. Synchronous programming functions as a one-track mind, checking off one task at a time in a rigid sequence.

Asynchronous programming allows more things to be done at the same time and is typically used to enhance the user experience by providing an effortless, quick-loading flow.

Synchronous programming is best utilized in reactive systems. While it is simpler for developers to code and is recognized by every programming language, sync is resource-intensive and can slow things down.

[This post was originally published by mendix](https://www.mendix.com/blog/asynchronous-vs-synchronous-programming/)
[other sources by outsystems](https://www.outsystems.com/blog/posts/asynchronous-vs-synchronous-programming/)
[other sources by freecodecamp](https://www.freecodecamp.org/news/synchronous-vs-asynchronous-in-javascript/)