Is the custom attribute event being triggered too soon?

My Unique Component Creation Journey
I have meticulously crafted a custom component to enhance the navigation of my application. The core structure consists of an ul element, with each li item dynamically generated based on the contents of the router's navigation list. This entire process unfolds within the attached event of the component, nothing too out of the ordinary.

Adding a Touch of Elegance
In pursuit of a visually appealing menu design, I decided to introduce a custom attribute into the root ul element of the component. Within the attached event of this custom attribute, my aim is to execute some DOM manipulations that would elevate the appearance of the menu to match those designed by trendsetting developers.

Navigating Through a Conundrum
Despite the fact that the attached event of the custom attribute gets triggered AFTER the attached event of the custom component, the dynamically created li elements are not yet present in the DOM during the execution of the attached event for the custom attribute.

A Question of Timing
My initial belief was that upon triggering the attached event, the view of the component would be attached to the DOM along with all preceding components. Consequently, once done with the attached event, any dynamically created HTML should also be incorporated into the DOM. Am I misguided in this assumption?

A Personal Reflection
While I am aware that employing the TaskQueue could potentially resolve my issue, I still remain curious if there exists an alternative approach or solution before resorting to such measures. My concern stems from the fear that manipulating time sequences may inadvertently lead me down a path of unforeseen challenges, resulting in a maintenance nightmare.

Answer №1

Let me clear up any confusion you may have about the TaskQueue.

If you're concerned about potential maintenance issues when moving tasks in time, that's a valid point when using setTimeout() because it introduces an actual delay and shifts execution to the next event loop. Even queueTask() operates similarly since it utilizes setTimeout() internally.

However, the TaskQueue's queueMicroTask() function functions differently.

Unlike queueTask() and setTimeout(), calling queueMicroTask() schedules the task for immediate execution on the same event loop. This method ensures a reliable execution order and is recommended to be used within the attached() method before manipulating the DOM.

Aurelia internally employs queueMicroTask() at various points, particularly in binding and templating-resources. Notable uses include:

  • Property- and collection observers utilize it to delay notifying subscribers until other bindings complete updating
  • The repeat attribute applies it to manage an ignoreMutations flag during inner collection updates

Consider two phases in the bind() and attached() hooks: one non-queued phase and one queued phase. The queued phase involves component operations dependent on the entire component graph being done with previous processes.

queueMicroTask() does not postpone execution; rather, it pushes it to the end of the call stack.

It essentially functions as placing the function callback at the end of the call stack without requiring complex setup. It's efficient and clean.

All li elements are dynamically generated based on the router's navigation list in the attached event of the component.

Keep in mind that anything created during attached() may not exist during another component's attached() due to compilation/composition order. This is especially crucial for custom attributes which heavily rely on TaskQueue for DOM completion.

Using queueMicroTask() guarantees:

  • Execution after Aurelia finishes its initial pass of attacheds and rendering
  • Immediate execution post-Aurelia completion without any delays

The most effective (and likely only correct) approach to address this matter is indeed through utilizing the TaskQueue - I assure you :)

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