How to Achieve Sequential Execution of setTimeout in JavaScript

Discover how to make setTimeout execute sequentially in JavaScript, overcoming asynchronous challenges with practical examples.
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How to Achieve Sequential Execution of setTimeout in JavaScript

Asynchronous programming in JavaScript can often lead to unexpected behaviors, especially if you're trying to control the order of execution. If you've ever worked with setTimeout, you might have noticed that all iterations of a loop can queue their callbacks to be executed simultaneously, which may not be the desired outcome. In this post, we'll tackle this common issue by demonstrating how to ensure the sequential execution of setTimeout using async/await.

The Problem

Consider the provided code where you want to execute a series of setTimeout operations such that each execution waits for the previous one to finish. Here's the relevant portion of the code:

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

In this code, the setTimeout function is called in a loop, leading to the issue where all timeouts start at once instead of in sequence.

The Solution

To achieve the desired sequential execution, we can utilize async/await in combination with Promise. This will allow us to pause the execution until the current timeout completes before moving to the next one.

Here’s how to modify the original code:

Steps to Modify the Code

Change the map to an async function: Modify the .map method to return a promise for each item in the matrix.

Resolve the promise inside the timeout: Ensure that the promise resolves only after the setTimeout finishes executing.

Revised Code Example

Below is the modified version of your function:

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

Explanation of the Revised Code

await new Promise(resolve => {...}): For every element of the matrix, we create a new promise which only resolves after the timeout has completed.

setTimeout(...): The actual delay is kept the same; however, the resolve is called only after the operation inside is completed.

Conclusion

With these modifications, you ensure that each setTimeout executes sequentially, thereby maintaining the desired order of operations in your asynchronous code. Handling asynchrony can be tricky in JavaScript, but by using promises along with async/await, you can create more manageable and predictable behavior in your applications.

Now you can enjoy the satisfaction of watching your patterns being displayed in sequence!