Simple pure Javascript drag controller slider

This code works in modern browsers. Just create some polyfill for that addEventListener and this custom range slider will be safe to use:

function rangeSlider(id, onDrag) {

    var range = document.getElementById(id),
        dragger = range.children[0],
        draggerWidth = 10, // width of your dragger
        down = false,
        rangeWidth, rangeLeft;

    dragger.style.width = draggerWidth + 'px';
    dragger.style.left = -draggerWidth + 'px';
    dragger.style.marginLeft = (draggerWidth / 2) + 'px';

    range.addEventListener("mousedown", function(e) {
        rangeWidth = this.offsetWidth;
        rangeLeft = this.offsetLeft;
        down = true;
        updateDragger(e);
        return false;
    });

    document.addEventListener("mousemove", function(e) {
        updateDragger(e);
    });

    document.addEventListener("mouseup", function() {
        down = false;
    });

    function updateDragger(e) {
        if (down && e.pageX >= rangeLeft && e.pageX <= (rangeLeft + rangeWidth)) {
            dragger.style.left = e.pageX - rangeLeft - draggerWidth + 'px';
            if (typeof onDrag == "function") onDrag(Math.round(((e.pageX - rangeLeft) / rangeWidth) * 100));
        }
    }

}

Example Usage

<style>
.range-slider {
  width:300px;
  height:20px;
  margin:0 auto 1em;
  position:relative;
  cursor:e-resize;
}
.range-slider:before {
  content:"";
  display:block;
  position:absolute;
  top:9px;
  left:0;
  width:100%;
  height:2px;
  background-color:black;
}
.range-slider span {
  display:block;
  height:inherit;
  position:relative;
  z-index:2;
  background-color:red;
  cursor:inherit;
}
</style>

<div class="range-slider" id="range-slider-1">
  <span></span>
</div>

<script>
rangeSlider('range-slider-1', function(value) {
    document.getElementById('test-area').innerHTML = value + '%';
});
</script>

Demo: http://jsbin.com/dulifezi/2/edit

---

Update

I’m creating a repo for this snippet here → https://github.com/taufik-nurrohman/range-slider

Take a look at DragDealer.js: https://skidding.github.io/dragdealer/

There's an example of changing opacity of an image based on the value of a slider here.

Hope this helps!