scroll to the top

by slawe

HTML

<div id="main">
    <span>Scroll Down ↓</span>
    <button type="button">To the top</button>
</div>

CSS

#main{
    display: block;
    position: relative;
    height: 4000px;
}

button{
    display:block;
    position: absolute;
    bottom:0;
}

JavaScript

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;
};