没有jQuery的返回页首按钮

Question

I want to create a button "Back to top" with javascript. My code (which I found on StackOverflow) does not work when I click the button nothing happens.

HTML

     <button type="button" id="backtotop_js">To the top</button>

JAVASCRIPT

     document.getElementById('backtotop_js').onclick = function () {
        scrollTo(document.documentElement, 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();
     }

     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'm using Chrome and Firefox)

Where's the mistake?

Answer 1

Will make the scroll to top without animation in vanilla JS

document.getElementById('backtotop_js').onclick = function () {    
    document.documentElement.scrollTop = 0;
}

EDIT: changed document.getElementsByTagName('body')[0] to document.documentElement as per Rudie's comment below.

Answer 2

Definition and Usage (of document.document.Element)

The documentElement property returns the documentElement of a document, as an Element object.

For HTML documents the returned object is the HTML element.

Note: If the HTML element is missing, the return value is null.

http://www.w3schools.com/jsref/prop_document_documentelement.asp

you shoud scroll not the html element but instead the body... as vikton was giving an example.