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24th December, 2022

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Difference Between Synchronous and Asynchronous Functions in JavaScript

In JavaScript, functions can be either synchronous or asynchronous. But what does this mean, and how does it affect the execution of your code? Let's take a closer look at the differences between these two types of functions.

Synchronous Functions

Synchronous functions are those that execute in a blocking manner, meaning that the code following the function will not be executed until the function has completed. An example of a synchronous function in JavaScript is the `alert()` function, which displays a message to the user and waits for them to click "OK" before continuing with the rest of the code.

Synchronous functions are easy to understand and can be useful for simple tasks, but they can also cause problems in certain situations. For example, if a synchronous function takes a long time to execute, it can cause the page to appear "frozen" or unresponsive to the user. This can be frustrating and may lead to a poor user experience.

One way to avoid this issue is to use asynchronous functions instead. But what are asynchronous functions, and how do they differ from synchronous functions?

Asynchronous Functions

Asynchronous functions, on the other hand, execute in a non-blocking manner. This means that the code following the function will be executed immediately, regardless of whether the function has completed. An example of an asynchronous function in JavaScript is the `setTimeout()` function, which executes a provided function after a specified number of milliseconds.

Asynchronous functions are useful for tasks that may take a long time to complete, such as making network requests or reading from a large file. By executing these tasks asynchronously, the page remains responsive to the user and the rest of the code can continue to run without being blocked.

To better understand the difference between synchronous and asynchronous functions, consider the following example:

   function getData() {
      // make network request
      // parse response
      // return data
   }

   function processData() {
      // process data
   }

   let data = getData();
   processData(data);

In this example, the `getData()` function represents a synchronous function that makes a network request and returns the data. The `processData()` function processes the data. If the `getData()` function takes a long time to complete, it will block the execution of the `processData()` function until it finishes. This means that the page will appear "frozen" or unresponsive to the user during this time.

To avoid this issue, we can use an asynchronous function to make the network request and return the data. For example:

   async function getData() {
      // make network request
      // parse response
      // return data
   }
function processData() {
// process data
}

let data = await getData();
processData(data);

In this revised example, the `getData()` function is an asynchronous function that returns a promise. The `await` keyword is used to wait for the promise to resolve before assigning the returned value to the `data` variable. This allows the `processData()` function to execute immediately, without being blocked by the network request.

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

Conclusion

In summary, the difference between synchronous and asynchronous functions in JavaScript is the way in which they execute and their impact on the rest of the code. Synchronous functions execute in a blocking manner, while asynchronous functions execute in a non-blocking manner. Understanding when to use synchronous or asynchronous functions is an important aspect of writing efficient and user-friendly JavaScript code.

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