I've been looking for a lightweight, dependency free dual slider for some time (it seemed crazy to import jQuery just for this) and there don't seem to be many out there. I ended up modifying @Wildhoney's code a bit and really like it.

function getVals(){
  // Get slider values
  var parent = this.parentNode;
  var slides = parent.getElementsByTagName("input");
    var slide1 = parseFloat( slides[0].value );
    var slide2 = parseFloat( slides[1].value );
  // Neither slider will clip the other, so make sure we determine which is larger
  if( slide1 > slide2 ){ var tmp = slide2; slide2 = slide1; slide1 = tmp; }
  
  var displayElement = parent.getElementsByClassName("rangeValues")[0];
      displayElement.innerHTML = slide1 + " - " + slide2;
}

window.onload = function(){
  // Initialize Sliders
  var sliderSections = document.getElementsByClassName("range-slider");
      for( var x = 0; x < sliderSections.length; x++ ){
        var sliders = sliderSections[x].getElementsByTagName("input");
        for( var y = 0; y < sliders.length; y++ ){
          if( sliders[y].type ==="range" ){
            sliders[y].oninput = getVals;
            // Manually trigger event first time to display values
            sliders[y].oninput();
          }
        }
      }
}

  section.range-slider {
    position: relative;
    width: 200px;
    height: 35px;
    text-align: center;
}

section.range-slider input {
    pointer-events: none;
    position: absolute;
    overflow: hidden;
    left: 0;
    top: 15px;
    width: 200px;
    outline: none;
    height: 18px;
    margin: 0;
    padding: 0;
}

section.range-slider input::-webkit-slider-thumb {
    pointer-events: all;
    position: relative;
    z-index: 1;
    outline: 0;
}

section.range-slider input::-moz-range-thumb {
    pointer-events: all;
    position: relative;
    z-index: 10;
    -moz-appearance: none;
    width: 9px;
}

section.range-slider input::-moz-range-track {
    position: relative;
    z-index: -1;
    background-color: rgba(0, 0, 0, 1);
    border: 0;
}
section.range-slider input:last-of-type::-moz-range-track {
    -moz-appearance: none;
    background: none transparent;
    border: 0;
}
  section.range-slider input[type=range]::-moz-focus-outer {
  border: 0;
}

<!-- This block can be reused as many times as needed -->
<section class="range-slider">
  <span class="rangeValues"></span>
  <input value="5" min="0" max="15" step="0.5" type="range">
  <input value="10" min="0" max="15" step="0.5" type="range">
</section>

NO jQuery solution

If you are not working with jQuery (like us) you would love this solution: https://refreshless.com/nouislider

Nice day