ScrollTo animation using pure javascript and no jquery

animatedScrollTo.js

document.getElementsByTagName('button')[0].onclick = function () {
   scrollTo(document.body, 0, 1250);   
}
    
function scrollTo(element, to, duration) {
    var start = element.scrollTop,
        change = to - start,
        currentTime = 0,
        increment = 20;
        
    var animateScroll = function(){        
        currentTime += increment;
        var val = Math.easeInOutQuad(currentTime, start, change, duration);
        element.scrollTop = val;
        if(currentTime < duration) {
            setTimeout(animateScroll, increment);
        }
    };
    animateScroll();
}

//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;
};

I also changed it to use performance.now():

var scrollTo = function(to, duration) {
    var element = document.scrollingElement || document.documentElement,
    start = element.scrollTop,
    change = to - start,
    startTs = performance.now(),
    // t = current time
    // b = start value
    // c = change in value
    // d = duration
    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;
    },
    animateScroll = function(ts) {
        var currentTime = ts - startTs;
        element.scrollTop = parseInt(easeInOutQuad(currentTime, start, change, duration));
        if(currentTime < duration) {
            requestAnimationFrame(animateScroll);
        }
        else {
            element.scrollTop = to;
        }
    };
    requestAnimationFrame(animateScroll);
};

For the utility if you just want to paste this around, here is minimized version of the requestAnimationFrame version:

var scrollTo=function(l,t){var c=document.scrollingElement||document.documentElement,m=c.scrollTop,a=l-m,s=performance.now(),i=function(o){var n,e,r=o-s;c.scrollTop=parseInt((n=r,e=m,o=a,(n/=t/2)<1?o/2*n*n+e:-o/2*(--n*(n-2)-1)+e)),r<t?requestAnimationFrame(i):c.scrollTop=l};requestAnimationFrame(i)};

Then use it like the others

scrollTo(150, 1000);

How would you go about making a linear function, no easing, just scroll down evenly in a set duration? Thank you!

@Alesvetina you would change the easing function for easeInOutQuad = function (t) { ... to simply this:

function (t) { return t; }

Here's An updated version that satisfies much more strict ESLint parameters, plus new ES syntax:

export const animateScrollTo = (to, duration) => {
  const element = document.scrollingElement || document.documentElement;
  const start = element.scrollTop;
  const change = to - start;
  const startDate = +new Date();
  // t = current time
  // b = start value
  // c = change in value
  // d = duration
  const easeInOutQuad = (t, b, c, d) => {
    let t2 = t;
    t2 /= d / 2;
    if (t2 < 1) return (c / 2) * t2 * t2 + b;
    t2 -= 1;
    return (-c / 2) * (t2 * (t2 - 2) - 1) + b;
  };
  const animateScroll = () => {
    const currentDate = +new Date();
    const currentTime = currentDate - startDate;
    element.scrollTop = parseInt(easeInOutQuad(currentTime, start, change, duration), 10);
    if (currentTime < duration) {
      requestAnimationFrame(animateScroll);
    } else {
      element.scrollTop = to;
    }
  };
  animateScroll();
};

Hi, an alternative version with top and left props (typescript).

 
const scrollTo = ({element, top, left, duration}: {
        element: HTMLElement, 
        top: number,
        left: number, 
        duration: number,    
    }) => {
        const startTop = element.scrollTop;
        const startLeft = element.scrollLeft;
        const changeTop = top - startTop;
        const changeLeft = left - startLeft;
        const startDate = new Date().getTime();

        const animateScroll = function(){
            const currentDate = new Date().getTime();
            const currentTime = currentDate - startDate;            
            element.scrollTop = easeInOutQuad(currentTime, startTop, changeTop, duration);
            element.scrollLeft = easeInOutQuad(currentTime, startLeft, changeLeft, duration);

            if(currentTime < duration) {
                requestAnimationFrame(animateScroll);
            } else {
                element.scrollTop = top;
                element.scrollLeft = left;
            }
        };
        animateScroll();
    }