How to Execute Code While a Promise is Resolving in JavaScript

Learn how to effectively manage asynchronous code execution in JavaScript by executing synchronous code while a promise is resolving.
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Understanding How to Execute Code While a Promise is Resolving in JavaScript

As a JavaScript developer, handling asynchronous operations is a fundamental skill. One common scenario involves executing certain pieces of code while a promise is still resolving. This guide will explore how you can manage this scenario effectively, ensuring your application remains responsive and efficiently processes tasks.

The Problem: Waiting for a Promise to Resolve

Imagine you have a function called foo() that returns a promise. You want to start foo() and execute some synchronous code while waiting for foo() to resolve. After foo() has resolved, you want to continue your code execution. The challenge here is how to achieve this flow without blocking the application and while ensuring your code executes in the correct sequence.

Example Scenario

Let’s take a basic outline of the flow you're trying to achieve:

Start the asynchronous function foo().

Execute some synchronous operations.

Once the promise resolves, continue with the remaining code.

The Solution: Using .then() to Handle Promise Resolution

Step 1: Start the Promise

The first step is to invoke the foo() function, but refrain from using await just yet. This allows the promise to start without halting the execution of further code:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Execute Synchronous Code

Following the promise invocation, you can perform synchronous operations. For example:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Handle Promise Resolution

To execute code after the promise resolves, you’ll need to use the .then() method on the promise. This method allows you to define what happens once the promise has successfully resolved:

[[See Video to Reveal this Text or Code Snippet]]

Putting it all together, you would have:

[[See Video to Reveal this Text or Code Snippet]]

Alternative Approach: Using async/await

If you're working in an environment that supports async/await, it's possible to streamline your code. Here’s how you can achieve the same logic with await:

Step 1: Await the Promise

You can merely ensure that the execution pauses until the promise resolves with await. However, the synchronous tasks need to be processed first, so ensure they come before the await:

[[See Video to Reveal this Text or Code Snippet]]

This makes your code cleaner and easier to read, especially when using async/await syntax.

Conclusion

In summary, handling multiple asynchronous processes in JavaScript can be straightforward if you utilize then() or async/await properly. By understanding how to invoke promises and execute synchronous operations simultaneously, you can ensure smoother performance and a more responsive user experience. Embrace these techniques in your coding practices, and watch your JavaScript skills grow!