JavaScript When and Done Function Understanding Their Use and Benefits

In this article, we’ll take a closer look at when() and done() functions and their use in JavaScript. These functions allow us to execute code when an asynchronous operation has completed.Thease function make it easier to manage complex asynchronous workflows.

We will discuss what these functions are, how they work, and their benefits in managing asynchronous code.

Web development frequently use JavaScript, a flexible programming language. The capability of JavaScript to run code asynchronously is one of its most powerful capabilities. Using asynchronous programming, we can complete several tasks at once without preventing the remaining portions of our code from running.

The biggest challenge with asynchronous code is management and debugging, particularly when numerous processes are running simultaneously.

When() Function

The when() function is used to execute code when multiple asynchronous operations have completed. It takes a list of promises as its arguments and returns a new promise that resolves when all the promises have been resolved.

The syntax for using the “when” function is as follows:

when(promise1, promise2, …, promiseN)
.then(function() {
// code to execute when all promises are resolved
});

The “when” function takes in one or more promises as arguments.

Let’s create a simple example of when() function with two promises:

var promise1 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 2000, 'promise1');
});

var promise2 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 3000, 'promise2');
});

when(promise1, promise2)
  .then(function() {
    console.log('Both promises resolved!');
  });

Here’s an example of using the when() function to execute code when multiple Ajax requests have been completed:

Example 2:

$.when($.ajax("/page1"), $.ajax("/page2"))
.done(function(result1, result2) {
// handle the results of both Ajax requests
});

In the above code, we use the jQuery library to make two Ajax requests to different URLs. We have passed these requests to the when() function as a parameter. The when returns a new promise that resolves when both Ajax requests have completed.

The done() function is then called with the results of both Ajax requests as its arguments.

Done() Function

The done() function is used to execute code when an asynchronous operation has completed successfully. It accepts a callback function as a parameter, which is executed when the promise is resolved.

The syntax for using the “done” function is as follows:

promise
.done(function() {
// code to execute when promise is resolved
});

Once the promise is resolved, the code inside the “done” method is executed.

Let’s create a sample example with done() function:

var promise = new Promise(function(resolve, reject) {
setTimeout(resolve, 2000, 'promise resolved');
});
promise
.then(function(result) {
console.log(result);
})
.catch(function(error) {
console.log(error);
})
.done(function() {
console.log('Promise complete!');
});

Here’s an example of using the done() function to execute code when an Ajax request has completed:

$.ajax("/page1")
.done(function(result) {
// handle the result of the Ajax request
});

In the above code, We call the done() function with a callback function that handles the result of the Ajax request. The callback function is executed when the promise is resolved.

Benefits of Using When() and Done() Functions

There are the following benefits of when() and done() functions when working with asynchronous code:

1. Better code organization: Both When() and done() functions make it easier to organize your asynchronous code. You can group related promises together and handle them in a single place.
2. Improved error handling: The done() function helps to handle errors that occur during an asynchronous operation. This allows you to write more robust and reliable code.
3. Simplified debugging: Both When() and done() functions make it easier to debug asynchronous code. You can use breakpoints to pause the execution of your code and inspect the state of your promises.

Conclusion

when() and done() functions are powerful methods for managing asynchronous code in JavaScript. They make it easier to handle multiple asynchronous operations and provide a more organized and reliable way to work with promises. It helps to write more efficient and maintainable code that is easier to debug and more resilient to errors.