Angular and setTimeout 0

1. Angular and setTimeout 0: Where does the love begin?

To understand why Angular and setTimeout 0 can’t live without each other, you first need to understand our protagonist. First, the “guy” Angular is a very famous client-side web application development framework, created and maintained by Google (True good boy IT salary 3k$). Meanwhile, “girl” setTimeout 0 is a function in JavaScript that allows us to execute a function after a specific amount of time, if set time is 0, the function will be executed immediately after all Existing functions have finished executing.

Let’s take a look at a basic example with setTimeout 0!

Surely you will notice that the result will be:

That’s interesting! Even though the setTimeout timeout is 0, the statement in the setTimeout function still waits for all previous statements to complete before being executed.

“So what does it have to do with Angular?” you may have questions. This is the interesting point! Angular uses a mechanism called Zone.js to monitor changes in the application and update the interface accordingly. But Zone.js tracks asynchronous operations through functions like setTimeout, Promise, XMLHttpRequest… Therefore, setTimeout 0 is an extremely useful “tool” for us to “squeeze”. Angular updates the interface instantly.

Now, let’s dive into the specific context of using setTimeout 0 in Angular!

2. Angular and setTimeout 0: An inseparable love affair

Let’s say you are working with an Angular application and you need to perform something after Angular has updated the interface, such as getting the size of a DOM element after it has been rendered. You might think, we just need to put that code in ngAfterViewInit() function, but no, life isn’t that simple, guys!

For example, see the following code:

When you run this code you will see that the height of the div is logged out before Angular actually renders it, hence the incorrect result. You can try changing the size of the div and see the result, it will surely surprise you!

“So how to solve this problem?” – You can ask. Yes, this is where the setTimeout 0 “girl” will come and rescue us!

Take a look at the following code:

By using setTimeout 0, we “force” Angular to wait for all current jobs to complete (including rendering our div) before doing the next. And now, when you run this code, you will see that the height of the div is logged out as you expected, no matter how you resize it.

That’s why I say Angular and setTimeout 0 can’t live without each other. This love affair not only helps us to solve difficult problems during application development, but also gives us deeper insights into how Angular works. You see, even programming, but still full of interesting love stories like this, right?

3. Note when using setTimeout 0 in Angular

Although this “love” may seem very romantic, it is not always passionate. It should be noted that using setTimeout 0 can lead to some problems if we are not careful.

Performance: SetTimeout will put your work in a queue and wait until all other jobs complete. If you use too much setTimeout 0, your application may become slower.

Memory Leaks: If you are not careful, using setTimeout can lead to memory leaks. This happens when you set the timeout but forgot to cancel it before the component is destroyed.

Unintended Side Effects: Because setTimeout 0 puts your work at the end of the queue, if there are any changes to the data you rely on in the meantime, the callback function may not work as expected. .

So how to avoid these problems? First, limit the use of setTimeout 0 to only when absolutely necessary. Second, always remember to cancel the timeout when it is no longer needed, especially when the component is destroyed.

Here is an example of how to cancel a timeout:

In this code, we store the ID of the timeout and then use it to cancel the timeout when the component is destroyed. This way, we can prevent memory leaks and ensure our applications are always performing at their best.

4. Conclusion

Angular and setTimeout 0, a romance but equally challenging. Although they can help us with many complex problems, care must also be taken to avoid possible problems. Hopefully after this article, you have a better understanding of how to use setTimeout 0 in Angular and how to make this “love” more peaceful. (Thanks for reading this far and trying to swallow the lines of a guy who never got more than 5 points in literature.)