Smooth Scroll to Anchor Vanilla JS

Smooth Scroll to Anchor Vanilla JS
Code Snippet:Smooth scrolling to anchor with pure javascript
Author: AciD
Published: January 11, 2024
Last Updated: January 22, 2024
Downloads: 2,957
License: MIT
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This Vanilla JS code snippet helps you to create a smooth scroll to anchor. It smoothly jumps to the section while clicking on the hash anchor. You can use this to create a table of contents or reference section.

How to Create Smooth Scroll to Anchor Vanilla JS

1. First of all, create the HTML structure as follows:

<div class="container">
	<div class="filler anchor" id="anchor1">anchor1</div>
	<div class="links">
		<a id="anchor1Link" href="#anchor1">Anchor 1</a>
		<a id="anchor2Link" href="#anchor2">Anchor 2</a>
		<a id="anchor3Link" href="#anchor3">Anchor 3</a>
		<a id="anchor4Link" href="#anchor4">Anchor 4</a>
	</div>
	<div class="longText">
		<p id="anchor2" class="anchor">anchor2 : This is a line, and there will be more after me.</p>
		<p id="anchor3" class="anchor">anchor3 : This is a line, and there will be more after me.</p>
		<p id="anchor4" class="anchor">anchor4 : This is a line, and there will be more after me.</p>
	</div>
	<div class="links">
		<a id="anchor1Link2" href="#anchor1">Anchor 1</a>
		<a id="anchor2Link2" href="#anchor2">Anchor 2</a>
		<a id="anchor3Link2" href="#anchor3">Anchor 3</a>
		<a id="anchor4Link2" href="#anchor4">Anchor 4</a>
	</div>
	<div class="filler"></div>
</div> 

2. After that, add the following CSS styles to your project:

.links {
  margin-top: 0.5rem;
  margin-bottom: 2rem;
}
.links a {
  font-size: 1.4rem;
  color: #006080;
  text-decoration: none;
  transition: color 0.5s ease, border-bottom 0.5s ease;
  border-bottom: 2px solid transparent;
}
.links a:hover {
  color: #646415;
  border-bottom: 2px solid yellow;
}
.links a:not(:last-of-type) {
  margin-right: 2rem;
}

.longText > p:last-of-type:after {
  content: "...or not ;)";
}

.anchor {
  color: lime;
  font-weight: bold;
}

p {
  margin: 0;
  text-align: center;
}

.container {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

a.button {
  color: yellow;
  text-decoration: none;
  transition: color 0.3s ease;
}
a.button:focus {
  outline: none;
}
a.button:hover {
  color: lime;
}

.button2 {
  background-color: deeppink;
  color: white;
  border: 1px solid red;
  border-radius: 2px;
  height: 30px;
  cursor: pointer;
  outline: none;
}
.button2:focus, .button2:active {
  outline: none;
}

3. Finally, add the following JavaScript code and done.

(function () {
  let d = document;

  function init() {
    //Links 
    let anchor1Link = d.getElementById('anchor1Link');
    let anchor2Link = d.getElementById('anchor2Link');
    let anchor3Link = d.getElementById('anchor3Link');
    let anchor4Link = d.getElementById('anchor4Link');
    let anchor1Link2 = d.getElementById('anchor1Link2');
    let anchor2Link2 = d.getElementById('anchor2Link2');
    let anchor3Link2 = d.getElementById('anchor3Link2');
    let anchor4Link2 = d.getElementById('anchor4Link2');
    //Anchors
    let anchor1 = d.getElementById('anchor1');
    let anchor2 = d.getElementById('anchor2');
    let anchor3 = d.getElementById('anchor3');
    let anchor4 = d.getElementById('anchor4');

    anchor1Link.addEventListener('click', e => {scrollTo(anchor1, e);}, false);
    anchor1Link2.addEventListener('click', e => {scrollTo(anchor1, e);}, false);
    anchor2Link.addEventListener('click', e => {scrollTo(anchor2, e);}, false);
    anchor2Link2.addEventListener('click', e => {scrollTo(anchor2, e);}, false);
    // anchor2Link.onclick = function() { scrollToSimple(document.documentElement, 500, 3000); }
    // anchor2Link2.onclick = function() { scrollToSimple(document.documentElement, 0, 3000); }
    anchor3Link.addEventListener('click', e => {scrollTo(anchor3, e);}, false);
    anchor3Link2.addEventListener('click', e => {scrollTo(anchor3, e);}, false);
    anchor4Link.addEventListener('click', e => {scrollTo(anchor4.offsetTop, e);}, false);
    anchor4Link2.addEventListener('click', e => {scrollTo(anchor4.offsetTop, e);}, false);

    console.log(anchor2); //DEBUG
    console.log('anchor1: ' + scrollTopValue(anchor1) + ' / ' + offsetTopValue(anchor1)); //DEBUG
    console.log('anchor2: ' + scrollTopValue(anchor2) + ' / ' + offsetTopValue(anchor2)); //DEBUG
    console.log('anchor3: ' + scrollTopValue(anchor3) + ' / ' + offsetTopValue(anchor3)); //DEBUG
    console.log('anchor4: ' + scrollTopValue(anchor4) + ' / ' + offsetTopValue(anchor4)); //DEBUG
    // d.addEventListener('scroll', (e) => { console.log(e) }, false); //DEBUG

    console.log('App loaded. Have fun!');
  }

  function scrollTopValue(domElement) {//DEBUG
    return 'scrollTopValue:', domElement.scrollTop;
  }
  function offsetTopValue(domElement) {//DEBUG
    return 'offsetTopValue:', domElement.offsetTop;
  }

  /*function scrollToSimple(element, to, duration) { //FIXME finish this
  	if (duration < 0) return;
  	var difference = to - element.offsetTop;
  	var perTick = difference / duration * 10;
  	console.log('perTick', perTick); //DEBUG
  		setTimeout(function() {
  		console.log('element.scrollTop:', element.scrollTop); //DEBUG
  		element.scrollTop += perTick;
  		console.log('element.scrollTop:', element.scrollTop); //DEBUG
  		scrollTo(element, to, duration - 10);
  	}, 10);
  }*/


  //cf. https://gist.github.com/james2doyle/5694700
  // requestAnimationFrame for Smart Animating https://goo.gl/sx5sts
  var requestAnimFrame = function () {
    return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function (callback) {
      window.setTimeout(callback, 1000 / 60);
    };
  }();

  function scrollTo(to, callback, duration = 1500) {//FIXME this always starts from '0', instead of the clicked element offsetTop -> This is because the position is calculated for the main <html> element, not the <iframe>'s <html> tag
    /*console.log('from:', from); //DEBUG
    // console.log('from.clientY:', from.clientY); //DEBUG
    // console.log('from.target.offsetTop:', from.target.offsetTop); //DEBUG
    
    // console.log('position():', document.documentElement.offsetTop || document.body.parentNode.offsetTop || document.body.offsetTop); //DEBUG
    // console.log('document.documentElement:', document.documentElement); //DEBUG
    // console.log('document.body:', document.body); //DEBUG
    let start;
    
    if (isMouseEvent(from)) { //FIXME : the scroll starts at the link, not where the screen really is : fix that
    	// start = from.target.offsetTop;
    	start = from.pageY; //FIXME
    }
    else {
    	start = from;
    }*/

    if (isDomElement(to)) {
      // console.log('this is an element:', to); //DEBUG
      to = to.offsetTop;
    }
    /*else {
    	// console.log('this is NOT an element:', to); //DEBUG
    }*/

    // because it's so fucking difficult to detect the scrolling element, just move them all
    function move(amount) {
      // document.scrollingElement.scrollTop = amount; //FIXME Test that
      document.documentElement.scrollTop = amount;
      document.body.parentNode.scrollTop = amount;
      document.body.scrollTop = amount;
    }

    function position() {
      return document.documentElement.offsetTop || document.body.parentNode.offsetTop || document.body.offsetTop;
    }

    var start = position(),
    change = to - start,
    currentTime = 0,
    increment = 20;
    console.log('start:', start); //DEBUG
    console.log('to:', to); //DEBUG
    console.log('change:', change); //DEBUG

    var animateScroll = function () {
      // increment the time
      currentTime += increment;
      // find the value with the quadratic in-out easing function
      var val = Math.easeInOutQuad(currentTime, start, change, duration);
      // move the document.body
      move(val);
      // do the animation unless its over
      if (currentTime < duration) {
        requestAnimFrame(animateScroll);
      } else
      {
        if (callback && typeof callback === 'function') {
          // the animation is done so lets callback
          callback();
        }
      }
    };

    animateScroll();
  }

  init();
})();

//-------------------- Unimportant js functions --------------------
// easing functions https://goo.gl/5HLl8
//t = current time
//b = start value
//c = change in value
//d = duration
Math.easeInOutQuad = function (t, b, c, d) {
  t /= d / 2;
  if (t < 1) {
    return c / 2 * t * t + b;
  }
  t--;
  return -c / 2 * (t * (t - 2) - 1) + b;
};

Math.easeInCubic = function (t, b, c, d) {
  var tc = (t /= d) * t * t;
  return b + c * tc;
};

Math.inOutQuintic = function (t, b, c, d) {
  var ts = (t /= d) * t,
  tc = ts * t;
  return b + c * (6 * tc * ts + -15 * ts * ts + 10 * tc);
};

function isDomElement(obj) {
  return obj instanceof Element;
}

function isMouseEvent(obj) {
  return obj instanceof MouseEvent;
}

function findScrollingElement(element) {//FIXME Test this too
  do {
    if (element.clientHeight < element.scrollHeight || element.clientWidth < element.scrollWidth) {
      return element;
    }
  } while (element = element.parentNode);
}

That’s all! hopefully, you have successfully integrated this smooth scroll to anchor code snippet into your project. If you have any questions or are facing any issues, please feel free to comment below.

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