How to create the Comparison Slider?

Learn how to create a Comparison Slider with CSS and JavaScript.

Demo:

Before & After:

What do you need to do?

Add HTML
Add CSS
Add JavaScript

Step1.

Add HTML

Add images that you want to compare:

<div class="img-comp-container">
  <div class="img-comp-img">
    <img src="https://lenadesign.org/wp-content/uploads/2021/04/make-up-1.jpg" width="640" height="480">
  </div>
  <div class="img-comp-img img-comp-overlay">
    <img src="https://lenadesign.org/wp-content/uploads/2021/04/no-make-up-1.jpg" width="640" height="480">
  </div>
</div>

Step2.

Add CSS

Set the colour and the position of the background and elements:

body {
  background-color: #eae2b7;
  display: flex; 
  align-items: center;
  justify-content: center;
  height: 100vh; 
}

.img-comp-container {
  left:-50px;
  position: relative;
  height: 480px; 
  width: 640px;
  border: 10px solid #e63946;
}

Set the position of the images:

.img-comp-img {
  position: absolute;
  width: auto;
  height: auto;
  overflow:hidden;
}

.img-comp-img img {
  display:block;
  vertical-align:middle;
}

Style the slider:

.img-comp-slider {
  position: absolute;
  cursor: ew-resize;
  width: 3px;
  height: 480px;
  background-color: white;
  color: white;
}

.img-comp-slider {
  position: absolute;
  cursor: ew-resize;
  width: 3px;
  height: 480px;
  background-color: white;
  color: white;
}

.img-comp-slider:before {
  content:"";
  position: absolute;
  content: url("https://lenadesign.org/wp-content/uploads/2021/04/dot-2.png");
  top:220px;
  left:-34px;  
}

.img-comp-slider:hover {
  box-shadow: 0 0 10px rgba(0,0,0,0.3); 
}

Step3.

Add JavaScript

function initComparisons() {
  var x, i;
  x = document.getElementsByClassName("img-comp-overlay");
  for (i = 0; i < x.length; i++) {
    compareImages(x[i]);
  }
  function compareImages(img) {
    var slider, img, clicked = 0, w, h;
    w = img.offsetWidth;
    h = img.offsetHeight;
    img.style.width = (w / 2) + "px";
    
    /*slider:*/
    slider = document.createElement("DIV");
    slider.style.zIndex = "10";
    slider.setAttribute("class", "img-comp-slider");
    img.parentElement.insertBefore(slider, img);
    slider.style.left = (w / 2) - (slider.offsetWidth / 2) + "px";
    slider.addEventListener("mousedown", slideReady);
    window.addEventListener("mouseup", slideFinish);
    slider.addEventListener("touchstart", slideReady);
    window.addEventListener("touchend", slideFinish);
    function slideReady(e) {
      
      e.preventDefault();
      clicked = 1;
      window.addEventListener("mousemove", slideMove);
      window.addEventListener("touchmove", slideMove);
    }
    function slideFinish() {
      clicked = 0;
    }
    function slideMove(e) {
      var pos;
      if (clicked == 0) return false;
      pos = getCursorPos(e)
      if (pos < 0) pos = 0;
      if (pos > w) pos = w;
      slide(pos);
    }
    function getCursorPos(e) {
      var a, x = 0;
      e = e || window.event;
      a = img.getBoundingClientRect();
      x = e.pageX - a.left;
      x = x - window.pageXOffset;
      return x;
    }
    function slide(x) {
      img.style.width = x + "px";
      slider.style.left = img.offsetWidth - (slider.offsetWidth / 2) + "px";
    }
  }
}

initComparisons();

Enjoy coding!

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