Proposal for performance improvement with Details component

with Vaadin 14.1.5 I had a performance issue with some forms (which included between 20 and 120 input/output elements plus containing layouts, details components with vertical layouts in it, …).
Opening a form took between 2 and 10 seconds, depending on browser (Firefox/Chromium took less, IE/Edge took more time).
The Browsers showed that nearly all the time was consumed with rendering, even when all the details-components where closed.

This was the code to create the details with vertical layouts in it (already with just opening the first details component only):

Details details = new Details();
details.setSummaryText("details name "+detailsnumber);
// Open the first and close all the others
details.setOpened(detailsnumber == 0);
verticalLayout.setVisible(detailsnumber == 0);

Reading I found one hint: “hide rarely used features (this also improves usability) when possible”.
So I added these lines and the loading time was reduced to ~ 0,5 seconds plus another 0,5-1 second for every detail component to open:

details.addOpenedChangeListener(new ComponentEventListener<Details.OpenedChangeEvent>() {
	public void onComponentEvent(OpenedChangeEvent event) {verticalLayout.setVisible(event.isOpened());}

I think that it would be great to add this as a standard behaviour to the details component.
Maybe as a special lazy loading mode:

Hi Sven!

Thanks for the suggestion. I agree, this would be a great feature to add. It also was part of the [original planning for this component]
( But since it’s a non-trivial thing to add it was postponed to later versions (not properly planned or scheduled yet).

Would be great if you can open a feature request describing your use case: