Better error message if Datepicker calendar is clicked after input is removed from DOM?

[alexdowad]

It can happen that after a non-inline Datepicker is opened, the <input> which the datepicker is "attached to" is removed from the DOM. When the user then clicks on the Datepicker calendar, an exception will be thrown with the message: "Missing instance data for this datepicker".

This is the relevant bit of code:

	/* Adjust one of the date sub-fields. */
	_adjustDate: function( id, offset, period ) {
		var target = $( id ),
			inst = this._getInst( target[ 0 ] );

Note that after retrieving target with $( id ), it is used right away without checking whether target.length > 0 or not. I would like to suggest it would be a good idea to make that check. If target is indeed empty, then an exception could be thrown with a more informative message.

(A web search reveals a lot of questions about the Missing instance data message; apparently it is challenging for a lot of users to understand what this message indicates.)

[mgol]

Thanks for the report. Does the issue you describe exist when jQuery UI 1.12.1 is used or only with jQuery UI 1.13.0 or newer?

[alexdowad]

@mgol Thanks for the question. I am not available to delve into this issue further, but the relevant code is still there on the current main branch:

jquery-ui/ui/widgets/datepicker.js

Lines 1028 to 1031 in 4bae79d

	/* Adjust one of the date sub-fields. */
	_adjustDate: function( id, offset, period ) {
	var target = $( id ),
	inst = this._getInst( target[ 0 ] );

[mgol]

Thanks, but we can't do much without a test case, especially that the UI team has limited resources now. See the project status at https://blog.jqueryui.com/2021/10/jquery-maintainers-update-and-transition-jquery-ui-as-part-of-overall-modernization-efforts/.