Saxon » SaxonJS

Do you have any kind of example for this? I can't reproduce it. OTOH, I also can't work out how to scroll an SVG. Everything I see on the web says that you should set scroll:overflow on the wrapper. AFAICT, an onwheel event doesn't cause any problems on a DIV.

https://chromestatus.com/feature/6662647093133312 suggests that with Chrome (and I think also Mozilla) wheel and similar at the window or document or document.body level are by default treated as passive.

And doesn't SaxonJS register event listeners you declare with mode="ixsl:onXXX" at the window or document level, meaning any use of ixsl:onwheel will have a listener created and subjected to the "default" passive setting Chrome imposes?

https://martin-honnen.github.io/xslt/2023/onwheel/sample1.html is a test case (just with HTML, no SVG used) that has e.g.

  <xsl:template match="div[@id = 'div1']" mode="ixsl:onwheel">
    <xsl:message select="saxon:timestamp() || ': ' || ixsl:event() => ixsl:get('type')"/>
  </xsl:template>

  <xsl:template match="div[@id = 'div1']" mode="ixsl:onmouseover">
    <xsl:message select="saxon:timestamp() || ': ' || ixsl:event() => ixsl:get('type')"/>
  </xsl:template>
  
  <xsl:template match="div[@id ='div2']" mode="ixsl:onwheel">
    <xsl:message select="saxon:timestamp() || ': ' || ixsl:event() => ixsl:get('type'), ixsl:event() => ixsl:call('preventDefault', [])"/>
  </xsl:template>

for which you can see in the browser console that SaxonJS sets up two document wide event listeners where the mouseover has passive as false but the wheel get the default passive as true and that way the attempt to call preventDefault causes Chrome to emit

[Intervention] Unable to preventDefault inside passive event listener due to target being treated as passive. See https://www.chromestatus.com/feature/6662647093133312

Thanks Martin :)

My code looks like this:

    <xsl:template match="svg:svg" mode="ixsl:onwheel">
        <xsl:sequence select="ixsl:call(ixsl:event(), 'preventDefault', [])"/>
        ...

Just to clarify what I was trying to do: prevent window scroll during onwheel and zoom the SVG in/out instead.

Ah, this is an issue in Chrome, not Firefox.

FWIW, it isn't that we set passive true, it's:

If not specified, defaults to false – except that in browsers other than Safari, defaults to true for the wheel, mousewheel, touchstart and touchmove events.

OK, so my question is then: how do I port the following JS code to SaxonJS? From https://codepen.io/osublake/pen/oGoyYb

window.addEventListener("wheel", onWheel);

function onWheel(event) {
  event.preventDefault();
  ...

Sorry. I wasn't suggesting that we don't need to fix this bug. I was just clarifying that it isn't the result of an explicit choice on our part, but rather a case of varying defaults. It's a bug, or at least an obviously missing feature, and we should fix it.

I'm sorry too, my comment wasn't meant to come accross as harsh :)

Hmm I'm not sure this helps to address my use case in the light of Martin's comment. I'll try to produce a test case.

I'm not sure what to suggest by way of a workaround for now. This is fixed for SaxonJS 3.0.

Do you have a citation for the 'passive by default' problem?

I tested the fix by verifying that an onwheel event generated console log errors in Chrome before I used the new feature to set passive to false, and not after I set it to false.

This is what Martin linked to earlier in the thread: Feature: Treat Document Level Wheel/Mousewheel Event Listeners as Passive

The wheel/mousewheel event listeners that are registered on document level targets (window.document, window.document.body, or window) will be treated as passive if not specified as otherwise and calling preventDefault() inside such listeners will be ignored.

OK so maybe it would work... I would need to test.