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ScrollTrigger firing setProperty event on page load not when trigger is reached

cotton test
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I've got a site that when sections scroll into view the wrapper background colour is changed depending on the data-attribute on said section. There's also a horizontal scrolling section which also updates the colours as they scroll into/out of view.


I'm using css vars to update the site text and menu/logo colours and these should be changed depending on the section data-copy attribute. However, this seems to update based on the first slide of the horizontal section on page load (there is a flash from black to white as you see the change on load), rather than as that section comes into view.


The markers seem to be in the correct place so I'm not sure why this would be triggering on load. Is it something to do with using vars and setProperty rather than just inline hex, the ```site_wrapper.style.backgroundColor = color;``` seems to work fine and when scrolling backwards all is ok (but that is probably because the onLeave etc has been set specifically)?




See the Pen wvyJOeQ by Cottonltd (@Cottonltd) on CodePen

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Hi @cotton. That's a lot of code to parse through in the demo. Are you saying that one of the onEnter callbacks is getting triggered when you don't think it should? Can you be a little more specific please? 


Please keep in mind that the containerAnimation must be pushed to the end initially and then put back to the beginning immediately (you'd never see that) in order for ScrollTrigger to accurately measure the distance it moves and set up the start/end trigger positions accurately. So perhaps that's related to what you're asking. 

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Sorry @GreenSock, kitchen sink demo as I wasn't sure which element may be causing issues.

I've reduced it down to core now and the onEnters that may be the issue. 


I think I've narrowed it down to the following that seems to be triggering too early (line 93 in codepen):


studysections.forEach((sct, i) => {
  const color = sct.getAttribute("data-color");
  const seccolor = sct.getAttribute("data-secondcolor");
  const textcolor = sct.getAttribute("data-text");

    containerAnimation: hCarousel,
    trigger: sct,
    start: "left center",
    end: "right center",
    scrub: true,
    onEnter: () => {
      site_wrapper.style.backgroundColor = color;
      site_wrapper.style.setProperty("--copycolor", textcolor);
      document.body.style.setProperty("--secondcolor", seccolor);
    onEnterBack: () => {
      site_wrapper.style.backgroundColor = color;
      site_wrapper.style.setProperty("--copycolor", textcolor);
      document.body.style.setProperty("--secondcolor", seccolor);

Its just the css vars that appear to be a problem, the secondary colour change early too but the background-color inline style is fine. Perhaps it's not GSAP at all...


It could well just be the containerAnimation problem, when you say 'pushed to the end' should I just call it at the end of the scripts or rearrange the DOM?


Thank you.



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Thanks, I see my demo was not on point.

It certainly is off at the start in there, on the full site it starts at zero.


I've forked the demo to include a left margin on the slides so the start point is inside the viewport and included a log of where the carousel container begins (0):

See the Pen xxYdbaJ by Cottonltd (@Cottonltd) on CodePen


On my local site, with the markers on the 'vertical position' ones show at first load (see screenshot attached), but then disappear to the horizontal section as soon as you begin scrolling and then reappear in place on the horizontal section. Feels like it's loading that carousel section first before the rest of the triggers are applied?



Screenshot 2022-05-18 at 16.09.30.png

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Yeah I see it and thought I'd fixed it on the fork but actually hadn't.

More speed, less haste required!


I've spent a bit more time on it and the above fork now acts more like the full site.

The log shows at 0 and the start marker shows at load, as well as the incorrect colour var, and disappears on initial scroll.


I hope this makes more sense and apologies for going round in circles!

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I'm still not totally following - you've got its left side at 0, but your start position is set to "left center" which means ScrollTrigger is doing exactly what it should by firing that onEnter. In other words, when the page loads, that element is already PAST the start position. See what I mean? 


I'm struggling a bit to understand exactly what you're asking here. Could you clarify? It'd definitely help if you simplified the demo so we don't have to weed through hundreds of lines of HTML/CSS/JS. Usually just a few colored <div> elements is ideal. 

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I think/hope I've diluted this enough now and apologies again for making it more confusing than it ought to be.


See the Pen YzeVaPp by Cottonltd (@Cottonltd) on CodePen


What I'm trying to do is to change the colour of the .global_block and background colour as sections scroll into view. This will be affected by both vertical and horizontal scrolling sections. However, as you noted, the first of the horizontal sections is already in view (i.e. has past 'left center') then it is triggering the colour change on page load (the block should be black on load).


I have three triggers working here:

1. The one that pins the horizontal section at 'top top'

2. one that changes the background colour (using a function that grabs the first and last slide colour attributes) as (1) reaches 'top center' and leaves at 'bottom center' — this has been removed for now to simplify the pen.

3. one that changes the colours as each slide section reaches 'left center'


So I guess my questions would now be:

– Can I make the first slide section start at 'left left' while the rest start at 'left center'

– Can I ignore the first and last slides of the horizontal section and use trigger (2) to update the colours onEnter and onLeave using another colour grab function

– Can I make the horizontal slides only trigger when that section comes into view rather than on page load?

– Any other options available




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  • Solution

Much easier to follow, thanks. 


Yeah, you can make the first one trigger at different spots, like this: 

See the Pen GRQEgWP?editors=0010 by GreenSock (@GreenSock) on CodePen


But that won't return it to black at the very top when you scroll backwards because of the way you've got the logic structured (there's no callback for onLeaveBack). You could simply use a paused timeline to serve as the controller for the colors and jump around to the appropriate time on that timeline, like this: 


See the Pen ExQXamX?editors=0010 by GreenSock (@GreenSock) on CodePen


Does that help? 

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