Scroll to position WITHIN a div (not window) using pure JS

Question

PURE JS ONLY PLEASE - NO JQUERY

I have a div with overflow scroll, the window (html/body) never overflows itself.

I have a list of anchor links and want to scroll to a position when they're clicked.

Basically just looking for anchor scrolling from within a div, not window.

window.scrollTo etc. don't work as the window never actually overflows.

Simple test case http://codepen.io/mildrenben/pen/RPyzqm

JADE

nav
  a(data-goto="#1") 1
  a(data-goto="#2") 2
  a(data-goto="#3") 3
  a(data-goto="#4") 4
  a(data-goto="#5") 5
  a(data-goto="#6") 6

main
  p(data-id="1") 1
  p(data-id="2") 2
  p(data-id="3") 3
  p(data-id="4") 4
  p(data-id="5") 5
  p(data-id="6") 6

SCSS

html, body {
  width: 100%;
  height: 100%;
  max-height: 100%;
}

main {
  height: 100%;
  max-height: 100%;
  overflow: scroll;
  width: 500px;
}

nav {
  background: red;
  color: white;
  position: fixed;
  width: 50%;
  left: 50%;
}

a {
  color: white;
  cursor: pointer;
  display: block;
  padding: 10px 20px;
  &:hover {
    background: lighten(red, 20%);
  }
}

p {
  width: 400px;
  height: 400px;
  border: solid 2px green;
  padding: 30px;
}

JS

var links = document.querySelectorAll('a'),
    paras = document.querySelectorAll('p'),
    main  = document.querySelector('main');

for (var i = 0; i < links.length; i++) {
  links[i].addEventListener('click', function(){
    var linkID = this.getAttribute('data-goto').slice(1);
    for (var j = 0; j < links.length; j++) {
      if(linkID === paras[j].getAttribute('data-id')) {
         window.scrollTo(0, paras[j].offsetTop); 
      }
    }
  })
}

PURE JS ONLY PLEASE - NO JQUERY

Answer 1

What you want is to set the scrollTop property on the <main> element.

var nav = document.querySelector('nav'),
    main  = document.querySelector('main');

  nav.addEventListener('click', function(event){
    var linkID,
      scrollTarget;
    if (event.target.tagName.toUpperCase() === "A") {
      linkID = event.target.dataset.goto.slice(1);
      scrollTarget = main.querySelector('[data-id="' + linkID + '"]');
      main.scrollTop = scrollTarget.offsetTop;
    }
  });

You'll notice a couple of other things I did different:

• I used event delegation so I only had to attach one event to the nav element which will more efficiently handle clicks on any of the links.
• Likewise, instead of looping through all the p elements, I selected the one I wanted using an attribute selector

This is not only more efficient and scalable, it also produces shorter, easier to maintain code.

This code will just jump to the element, for an animated scroll, you would need to write a function that incrementally updates scrollTop after small delays using setTimeout.

var nav = document.querySelector('nav'),
    main  = document.querySelector('main'),
    scrollElementTo = (function () {
      var timerId;
      return function (scrollWithin, scrollTo, pixelsPerSecond) {
        scrollWithin.scrollTop = scrollWithin.scrollTop || 0;
        var pixelsPerTick = pixelsPerSecond / 100,
          destY = scrollTo.offsetTop,
          direction = scrollWithin.scrollTop < destY ? 1 : -1,
          doTick = function () {
            var distLeft = Math.abs(scrollWithin.scrollTop - destY),
              moveBy = Math.min(pixelsPerTick, distLeft);
            scrollWithin.scrollTop += moveBy * direction;
            if (distLeft > 0) {
              timerId = setTimeout(doTick, 10);
            }
          };
        clearTimeout(timerId);
        doTick();
      };
    }());

nav.addEventListener('click', function(event) {
  var linkID,
    scrollTarget;
  if (event.target.tagName.toUpperCase() === "A") {
    linkID = event.target.dataset.goto.slice(1);
    scrollTarget = main.querySelector('[data-id="' + linkID + '"]');
    scrollElementTo(main, scrollTarget, 500);
  }
});

Another problem you might have with the event delegation is that if the a elements contain child elements and a child element is clicked on, it will be the target of the event instead of the a tag itself. You can work around that with something like the getParentAnchor function I wrote here.