Detect/measure scroll speed

Question

I\'m trying to think of a way to measure the velocity of a scroll event, that would produce some sort of a number which will represent the speed (d

Answer 1

var checkScrollSpeed = (function(settings){
    settings = settings || {};

    var lastPos, newPos, timer, delta, 
        delay = settings.delay || 50; // in "ms" (higher means lower fidelity )

    function clear() {
      lastPos = null;
      delta = 0;
    }

    clear();

    return function(){
      newPos = window.scrollY;
      if ( lastPos != null ){ // && newPos < maxScroll 
        delta = newPos -  lastPos;
      }
      lastPos = newPos;
      clearTimeout(timer);
      timer = setTimeout(clear, delay);
      return delta;
    };
})();

// listen to "scroll" event
window.onscroll = function(){
  console.log( checkScrollSpeed() );
};

Demo page: http://codepen.io/vsync/pen/taAGd/

Simplified demo: http://jsbin.com/mapafadako/edit?js,console,output

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For real fun, give a real website these rules, then copy the JS and run it