MousePosition: allow rendering of empty string

[JakobMiksch]

fixes #12482

ol.control.MousePosition
This PR makes it possible to enter an empty string '' as undefinedHTML value. This will finally add an empty string into the target HTML element. The behavior before was that an empty string was recognized as falsey and therefore the default value - a whitespace - was used in the target HTML element.

[tschaub]

The tests make it look like the current behavior is intentional:

openlayers/test/browser/spec/ol/control/mouseposition.test.js

Line 108 in bfe5afe

it('retains the mouse position when undefinedHTML is falsey and mouse moves outside the viewport', function () {

[MoonE]

See #8109 for the PR introducing the current behavior.

[tschaub]

An alternative would be to render an empty element instead of a non-breaking space by default. This would not break applications that are relying on the current documented/tested behavior with respect to undefinedHTML: ''. But it would potentially break styling if an application is relying on the element always having text content (which I think is why the non-breaking space was added).

[tschaub]

Thanks for the reminder, @MoonE . After reading through #8109 and #2914, I think this pull request makes sense (maybe a breaking change, but maybe a fix).

If you want to clear the control on mouseout, use the default options (same as undefinedHTML: ' ').

If you want to retain the position on mouseout, pass undefinedHTML: undefined.

If you want to clear the position by rendering an empty element instead of a non-breaking space, pass undefinedHTML: ''.

Kind of subtle and awkward (but I think that is mostly due to the undefinedHTML name).

[tschaub]

@JakobMiksch can you update the tests to cover the new behavior (change existing test for empty string and add test for undefined)?

[marcjansen]

While we are at it, maybe also change the name from undefinedHTML to sth. less confusing?

[tschaub]

While we are at it, maybe also change the name from undefinedHTML to sth. less confusing?

I had placeholder in mind (inspired by <input placeholder="foo">). But we might want to wait for a major release for that. Or we could add placeholder, deprecate undefinedHTML, and then later remove it.

[tschaub]

@JakobMiksch can you update the tests to cover the new behavior (change existing test for empty string and add test for undefined)?

I pushed new tests in 9e7f5a9.

[tschaub]

Thanks for the contribution, @JakobMiksch

[tschaub]

While we are at it, maybe also change the name from undefinedHTML to sth. less confusing?

@marcjansen - see #12491. The change there restores the previous (awkward) behavior of undefinedHTML and adds a new placeholder option. This placeholder option can be set to the empty string to render the empty string when the mouse position is not available.

[JakobMiksch]

@tschaub thanks for finalizing this PR. I would have tried soon, but you were faster 👍