Set default date for zul datebox

I inherited a legacy website written in old zul and have to add new datebox component for birthday datepicker.

Have added a constraint to accept dates before a given date but that triggers an error alertbox from start as the date presented/selected by default on the datepicker is today.

I wouldn't want to use a workaround but to all due respect it seems like this is something over the top feature I'm looking for in zk's reality:

The main showcase for zul does include a birthday datebox, but pretty lame as it doesn't contain any constrain on age.
There is zk fiddler to show how the before constrain works, but that just proves my point that it doesn't select the first proper date for default date at least, if there is no clean way of setting it.
There is forum post that proposes a workaround to set the default year, so Zk is most probably incapable of doing this without a workaround.
There is an open ZK Jira issue from 2017 that addresses somewhat this issue, with a proposed solution pretty much the same as the workaround mentioned in the above point - so the hope is kinda lost, have to go on the workaround route.

I did try that workaround (after the forum post, as that has default year), but the workaround doesn't work for me. It does execute the

this.setValue(initialDate);

And I see that the value is set into the datebox's _pop/_value and _pop/_end nodes but no difference is visible on the datepicker box, still today is preselected altough it is greyed out - so no effect. Still, when I try it in a fiddle with version 6.5.8.1, the oldest engine that exists, it does work, but not locally with v5.0.11.

In the buglist for this version there is no mention of datebox. Tried to look into to some bugs that might be interfering but turns out it was just another episode of me wasting time with this.

Tried in the 5.0.11 sandbox and it doesnt work with that version. The structure of how I use it is imitated in the linked fiddler. Hints on a workaround that works on this version?

Solution

ZK 5.0.11 is a bit on the older side currently, so it might not accept exactly the same overrides as later versions. If I understand the issue correctly, it boils down to either

1 - setting a value before Datebox is rendered to have a "initial date" opened in calendar.

I'd say that's the easy way out, since you can use either composing or databinding to set the value of the datebox during page rendering. Here's a small sample using databinding and zscripts, but the same logic should apply from composer with setValue(). You mentioned that this doesn't work for you locally with 5.0.11 though. Can you share the code that you are using for this? Sample code here in fiddle I can run it on local 5.0.11, and it set the date before popup is opened.

2 - setting an initial date (which doesn't affect the selected value) but would be the target for the opened calendar.

This is not a default ZK 5 behavior for datebox. If you want that effect, you would need to customize it using an override script. Simplest way in can think of in ZK 5 is to use the open event of the datebox popup here's an example of what it would look like (package in a script tag in a single page for the example, would use a global js file for real deployement) example here