Before After Comparison Slider With Touch Support

A Vanilla JavaScript mobile-friendly before/after comparison slider to view the difference between two images with mouse move and touch swipe events.

How to use it:

1. Insert before/after images to the comparison slider as follows:

<div id="example" class="bal-container">
  <div class="bal-after">
    <img src="after.jpg">
    <div class="bal-afterPosition afterLabel">
      After
    </div>
  </div>
  <div class="bal-before">
    <div class="bal-before-inset">
    <img src="before.jpg">
      <div class="bal-beforePosition beforeLabel">
        Before
      </div>
    </div>
  </div>
  <div class="bal-handle">
    <span class=" handle-left-arrow"></span>
    <span class="handle-right-arrow"></span>
  </div>
</div>

2. The main CSS styles for the comparison slider.

.bal-container {
    position: relative;
    width: 100%;
    height: 100%;
    cursor: grab;
    overflow: hidden;
}
.bal-after {
    display: block;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100%;
    overflow: hidden;
}
.bal-before {
    display: block;
    position: absolute;
    top: 0;
    /* right: 0; */
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 15;
    overflow: hidden;
}
.bal-before-inset {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
}
.bal-after img,
.bal-before img {
    object-fit: cover;
    position: absolute;
    width: 100%;
    height: 100%;
    object-position: 50% 50%;
    top: 0;
    bottom: 0;
    left: 0;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -o-user-select: none;
    user-select: none;
}
.bal-beforePosition {
    background: #121212;
    color: #fff;
    left: 0;
    pointer-events: none;
    border-radius: 0.2rem;
    padding: 2px 10px;
}
.bal-afterPosition {
    background: #121212;
    color: #fff;
    right: 0;
    pointer-events: none;
    border-radius: 0.2rem;
    padding: 2px 10px;
}
.beforeLabel {
    position: absolute;
    bottom: 0;
    margin: 1rem;
    font-size: 1em;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -o-user-select: none;
    user-select: none;
}
.afterLabel {
    position: absolute;
    bottom: 0;
    margin: 1rem;
    font-size: 1em;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -o-user-select: none;
    user-select: none;
}

3. Style the slider handle & arrows.

.bal-handle {
    height: 41px;
    width: 41px;
    position: absolute;
    left: 50%;
    top: 50%;
    margin-left: -20px;
    margin-top: -21px;
    border: 2px solid #fff;
    border-radius: 1000px;
    z-index: 20;
    pointer-events: none;
    box-shadow: 0 0 10px rgb(12, 12, 12);
}
.handle-left-arrow,
.handle-right-arrow {
    width: 0;
    height: 0;
    border: 6px inset transparent;
    position: absolute;
    top: 50%;
    margin-top: -6px;
}
.handle-left-arrow {
    border-right: 6px solid #fff;
    left: 50%;
    margin-left: -17px;
}
.handle-right-arrow {
    border-left: 6px solid #fff;
    right: 50%;
    margin-right: -17px;
}
.bal-handle::before {
    bottom: 50%;
    margin-bottom: 20px;
    box-shadow: 0 0 10px rgb(12, 12, 12);
}
.bal-handle::after {
    top: 50%;
    margin-top: 20.5px;
    box-shadow: 0 0 5px rgb(12, 12, 12);
}
.bal-handle::before,
.bal-handle::after {
    content: " ";
    display: block;
    width: 2px;
    background: #fff;
    height: 9999px;
    position: absolute;
    left: 50%;
    margin-left: -1.5px;
}

4. Load the main script at the end of the document.

<script src="js/script.js"></script>

5. Initialize the before after comparison slider. That’s it.

new BeforeAfter({
    id: '#one'
});