Have you ever clicked on an image on a webpage that opens up a larger version of the image with navigation to view other photos?

Some folks call it a pop-up. Others call it a lightbox. Bootstrap calls it a modal. I mention Bootstrap because I want to use it to make the same sort of thing. So, let’s call it a modal from here on out.

Why Bootstrap? you might ask. Well, a few reasons:

• I’m already using Bootstrap on the site where I want this effect, so there’s no additional overhead in terms of loading resources.
• I want something where I have complete and easy control over aesthetics. Bootstrap is a clean slate compared to most modal plugins I’ve come across.
• The functionality I need is fairly simple. There isn’t much to be gained by coding everything from scratch. I consider the time I save using the Bootstrap framework to be more beneficial than any potential drawbacks.

Here’s where we’ll end up:

Let’s go through that, bit by bit.

Step 1: Create the image gallery grid

Let’s start with the markup for a grid layout of images. We can use Bootstrap’s grid system for that.

<div class="row" id="gallery">
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-1">
  </div>
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-2">
  </div>
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-3">
  </div>
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-4">
  </div>
</div>

Now we need data attributes to make those images interactive. Bootstrap looks at data attributes to figure out which elements should be interactive and what they should do. In this case, we’ll be creating interactions that open the modal component and allow scrolling through the images using the carousel component.

About those data attributes:

1. We’ll add data-toggle="modal"  and data-target="#exampleModal" to the parent element (#gallery). This makes it so clicking anything in the gallery opens the modal. We should also add the data-target value (#exampleModal) as the ID of the modal itself, but we’ll do that once we get to the modal markup.
2. Let’s add data-target="#carouselExample"  and a data-slide-to attribute to each image. We could add those to the image wrappers instead, but we’ll go with the images in this post. Later on, we’ll want to use the data-target value (#carouselExample) as the ID for the carousel, so note that for when we get there. The values for data-slide-to are based on the order of the images.

Here’s what we get when we put that together:

<div class="row" id="gallery" data-toggle="modal" data-target="#exampleModal">
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-1.jpg" data-target="#carouselExample" data-slide-to="0">
  </div>
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-2.jpg" data-target="#carouselExample" data-slide-to="1">
  </div>
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-3.jpg" data-target="#carouselExample" data-slide-to="2">
  </div>
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-4.jpg" data-target="#carouselExample" data-slide-to="3">
  </div>
</div>

Interested in knowing more about data attributes? Check out the CSS-Tricks guide to them.

Step 2: Make the modal work

This is a carousel inside a modal, both of which are standard Bootstrap components. We’re just nesting one inside the other here. Pretty much a straight copy-and-paste job from the Bootstrap documentation.

Here’s some important parts to watch for though:

1. The modal ID should match the data-target of the gallery element.
2. The carousel ID should match the data-target of the images in the gallery.
3. The carousel slides should match the gallery images and must be in the same order.

Here’s the markup for the modal with our attributes in place:

<!-- Modal markup: https://getbootstrap.com/docs/4.4/components/modal/ -->
<div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-hidden="true">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">×</span>
        </button>
      </div>
      <div class="modal-body">
        
      <!-- Carousel markup goes here -->


      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
      </div>
    </div>
  </div>
</div>

We can drop the carousel markup right in there, Voltron style!

<!-- Modal markup: https://getbootstrap.com/docs/4.4/components/modal/ -->
<div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-hidden="true">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">×</span>
        </button>
      </div>
      <div class="modal-body">
        
      <!-- Carousel markup: https://getbootstrap.com/docs/4.4/components/carousel/ -->
      <div id="carouselExample" class="carousel slide" data-ride="carousel">
          <div class="carousel-inner">
            <div class="carousel-item active">
              <img class="d-block w-100" src="/image-1.jpg">
            </div>
            <div class="carousel-item">
              <img class="d-block w-100" src="/image-2.jpg">
            </div>
            <div class="carousel-item">
              <img class="d-block w-100" src="/image-3.jpg">
            </div>
            <div class="carousel-item">
              <img class="d-block w-100" src="/image-4.jpg">
            </div>
          </div>
          <a class="carousel-control-prev" href="#carouselExample" role="button" data-slide="prev">
            <span class="carousel-control-prev-icon" aria-hidden="true"></span>
            <span class="sr-only">Previous</span>
          </a>
          <a class="carousel-control-next" href="#carouselExample" role="button" data-slide="next">
            <span class="carousel-control-next-icon" aria-hidden="true"></span>
            <span class="sr-only">Next</span>
          </a>
        </div>
      </div>

      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
      </div>
    </div>
  </div>
</div>

Looks like a lot of code, right? Again, it’s basically straight from the Bootstrap docs, only with our attributes and images.

Step 3: Deal with image sizes

This isn’t necessary, but if the images in the carousel have different dimensions, we can crop them with CSS to keep things consistent. Note that we’re using Sass here.

// Use Bootstrap breakpoints for consistency.
$bootstrap-sm: 576px;
$bootstrap-md: 768px;
$bootstrap-lg: 992px;
$bootstrap-xl: 1200px;


// Crop thumbnail images.
#gallery {
  img {
    height: 75vw;
    object-fit: cover;
    
    @media (min-width: $bootstrap-sm) {
      height: 35vw;
    }
    
    @media (min-width: $bootstrap-lg) {
      height: 18vw;
    }
  }
}


// Crop images in the coursel
.carousel-item {
  img {
    height: 60vw;
    object-fit: cover;
    
    @media (min-width: $bootstrap-sm) {
      height: 350px;
    }
  }
}

Step 4: Optimize the images

You may have noticed that the markup uses the same image files in the gallery as we do in the modal. That doesn’t need to be the case. In fact, it’s a better idea to use smaller, more performant versions of the images for the gallery. We’re going to be blowing up the images to their full size version anyway in the modal, so there’s no need to have the best quality up front.

The good thing about Bootstrap’s approach here is that we can use different images in the gallery than we do in the modal. They’re not mutually exclusive where they have to point to the same file.

So, for that, I’d suggest updating the gallery markup with lower-quality images:

<div class="row" id="gallery" data-toggle="modal" data-target="#exampleModal">
  <div class="col-12 col-sm-6 col-lg-3">
    <img class="w-100" src="/image-1-small.jpg" data-target="#carouselExample" data-slide-to="0">
  
  <!-- and so on... -->
</div>

That’s it!

The site where I’m using this has already themed Bootstrap. That means everything is already styled to spec. That said, even if you haven’t themed Bootstrap you can still easily add custom styles! With this approach (Bootstrap vs. plugins), customization is painless because you have complete control over the markup and Bootstrap styling is relatively sparse.

Here’s the final demo: