javascript - Why does ScrollTop position not work on mobile Safari? - Stack Overflow

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I have a feature on my website where the logo scrolls vertically depending on the users position on the site.

You can see it working on Chrome here

However it does not work on Safari, which includes mobile and tablet.

The scroll position does not seem to change at all in the console.

// logo positioning  

let logos, logoHeight, barTopMargin;
let viewportHeight;

window.addEventListener('load', init);
window.addEventListener('resize', setSizes);
document.addEventListener('scroll', update);


function init(lockUpdate) {
    logos = document.querySelectorAll('.scroll-text');
    setSizes(lockUpdate);
}

function update() {
    // ensure initialization and prevent recursive call
    if (!logos) init(true);
    //*************************************************

    /**************************************************
        THIS LINE MUST BE HERE.
    **************************************************/
    let maxScrollDist  = document.documentElement.scrollHeight - viewportHeight;
    //*************************************************

    let currentScrollPos = document.documentElement.scrollTop;
    let newTop;

    let middle = currentScrollPos + viewportHeight/2;
    let middleY = maxScrollDist/2;

    if (middle >= (maxScrollDist+viewportHeight)/2) {
        let p = (middleY - Math.floor(middle - (maxScrollDist+viewportHeight)/2))*100/middleY;

        newTop = viewportHeight/2 - logoHeight/2;
        newTop += (100-p)*(viewportHeight/2)/100;
        newTop -= (100-p)*(barTopMargin +logoHeight/2)/100;
        newTop = Math.max(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    } else {
        let p = (middleY - Math.floor(-middle + (maxScrollDist+viewportHeight)/2))*100/middleY;
        newTop = barTopMargin*(100-p)/100+(viewportHeight/2 - (logoHeight/2)*p/100 )*p/100;
        newTop = Math.min(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    }

    logos.forEach(function(el) {
        el.style.top = newTop + "px";
    });
}

function setSizes(lockUpdate) {
    logoHeight     = logos[0].offsetHeight;
    barTopMargin   = parseInt(getComputedStyle(document.querySelector('#page'), '::before').top);
    viewportHeight = window.innerHeight;
    if (lockUpdate === true) return;
    update();
}

I have a feature on my website where the logo scrolls vertically depending on the users position on the site.

You can see it working on Chrome here

However it does not work on Safari, which includes mobile and tablet.

The scroll position does not seem to change at all in the console.

// logo positioning  

let logos, logoHeight, barTopMargin;
let viewportHeight;

window.addEventListener('load', init);
window.addEventListener('resize', setSizes);
document.addEventListener('scroll', update);


function init(lockUpdate) {
    logos = document.querySelectorAll('.scroll-text');
    setSizes(lockUpdate);
}

function update() {
    // ensure initialization and prevent recursive call
    if (!logos) init(true);
    //*************************************************

    /**************************************************
        THIS LINE MUST BE HERE.
    **************************************************/
    let maxScrollDist  = document.documentElement.scrollHeight - viewportHeight;
    //*************************************************

    let currentScrollPos = document.documentElement.scrollTop;
    let newTop;

    let middle = currentScrollPos + viewportHeight/2;
    let middleY = maxScrollDist/2;

    if (middle >= (maxScrollDist+viewportHeight)/2) {
        let p = (middleY - Math.floor(middle - (maxScrollDist+viewportHeight)/2))*100/middleY;

        newTop = viewportHeight/2 - logoHeight/2;
        newTop += (100-p)*(viewportHeight/2)/100;
        newTop -= (100-p)*(barTopMargin +logoHeight/2)/100;
        newTop = Math.max(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    } else {
        let p = (middleY - Math.floor(-middle + (maxScrollDist+viewportHeight)/2))*100/middleY;
        newTop = barTopMargin*(100-p)/100+(viewportHeight/2 - (logoHeight/2)*p/100 )*p/100;
        newTop = Math.min(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    }

    logos.forEach(function(el) {
        el.style.top = newTop + "px";
    });
}

function setSizes(lockUpdate) {
    logoHeight     = logos[0].offsetHeight;
    barTopMargin   = parseInt(getComputedStyle(document.querySelector('#page'), '::before').top);
    viewportHeight = window.innerHeight;
    if (lockUpdate === true) return;
    update();
}

• javascript
• safari
• scrolltop

Share Improve this question Follow edited Nov 17, 2019 at 23:59 n1stre 6,09644 gold badges2323 silver badges4242 bronze badges asked Nov 4, 2019 at 12:22 Mr ToadMr Toad 25622 gold badges1414 silver badges4646 bronze badges 3

• Possible duplicate of stackoverflow./questions/1830080/… – Prabhjot Singh Kainth Commented Nov 15, 2019 at 15:55
• Have a look at some of these suggestions: github./nuxt/nuxt.js/issues/2512 – Brett Gregson Commented Nov 15, 2019 at 15:55
• Thanks Brett - I did actually look at this, but unfortunately I don't understand JS or the syntax enough to know HOW to apply this information. – Mr Toad Commented Nov 20, 2019 at 12:48

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 6 +100

The reason behind this behavior is laid inside the difference in scrolling implementation between the browsers. For example Chrome calculates page scrolling based on the <html>, while Safari does the same on the <body>.

Chrome:

Safari:

Considering this info it would reasonable to assume that in Safari document.documentElement is pletely unaware of page global scrolling value.

And to fix this issue you could define a helper func that uses document.scrollingElement with fallback to getBoundingClientRect on document.documentElement:

function getScrollingElement() {
  if (document.scrollingElement) {
    return document.scrollingElement;
  }

  const docElement = document.documentElement;
  const docElementRect = docElement.getBoundingClientRect();

  return {
    scrollHeight: Math.ceil(docElementRect.height),
    scrollTop: Math.abs(docElementRect.top)
  }
}

and use it in your update func:

function update() {
  // ensure initialization and prevent recursive call
  if (!logos) init(true);
  //*************************************************

  /**************************************************
      THIS LINE MUST BE HERE.
  **************************************************/
  let maxScrollDist = getScrollingElement().scrollHeight - viewportHeight;
  //*************************************************

  let currentScrollPos = getScrollingElement().scrollTop;

  // ...
}

function getScrollingElement() {
  // ...
}

Full code:

// logo positioning  

let logos, logoHeight, barTopMargin;
let viewportHeight;

window.addEventListener('load', init);
window.addEventListener('resize', setSizes);
document.addEventListener('scroll', update);


function init(lockUpdate) {
    logos = document.querySelectorAll('.scroll-text');
    setSizes(lockUpdate);
}

function update() {
    // ensure initialization and prevent recursive call
    if (!logos) init(true);
    //*************************************************

    /**************************************************
        THIS LINE MUST BE HERE.
    **************************************************/
    let maxScrollDist  = getScrollingElement().scrollHeight - viewportHeight;
    //*************************************************

    let currentScrollPos = getScrollingElement().scrollTop;
    let newTop;

    let middle = currentScrollPos + viewportHeight/2;
    let middleY = maxScrollDist/2;

    if (middle >= (maxScrollDist+viewportHeight)/2) {
        let p = (middleY - Math.floor(middle - (maxScrollDist+viewportHeight)/2))*100/middleY;

        newTop = viewportHeight/2 - logoHeight/2;
        newTop += (100-p)*(viewportHeight/2)/100;
        newTop -= (100-p)*(barTopMargin +logoHeight/2)/100;
        newTop = Math.max(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    } else {
        let p = (middleY - Math.floor(-middle + (maxScrollDist+viewportHeight)/2))*100/middleY;
        newTop = barTopMargin*(100-p)/100+(viewportHeight/2 - (logoHeight/2)*p/100 )*p/100;
        newTop = Math.min(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    }

    logos.forEach(function(el) {
        el.style.top = newTop + "px";
    });
}

function getScrollingElement() {
  if (document.scrollingElement) {
    return document.scrollingElement;
  }

  const docElement = document.documentElement;
  const docElementRect = docElement.getBoundingClientRect();

  return {
    scrollHeight: Math.ceil(docElementRect.height),
    scrollTop: Math.abs(docElementRect.top)
  }
}

function setSizes(lockUpdate) {
    logoHeight     = logos[0].offsetHeight;
    barTopMargin   = parseInt(getComputedStyle(document.querySelector('#page'), '::before').top);
    viewportHeight = window.innerHeight;
    if (lockUpdate === true) return;
    update();
}

Hope this helps.

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