In modern web design, creating interactive and visually engaging user experiences is crucial. One popular feature that has gained traction over time is the Before After Image Slider. This tool allows users to compare two images by simply dragging a slider back and forth. It’s particularly useful for showcasing transformations, such as renovations, product improvements, or even comparing various stages of a project.

Imagine you’re browsing through a website showcasing a makeup brand. A Before After Image Slider allows you to seamlessly compare the difference between a model’s bare face and the same model after applying makeup. This feature is not only visually appealing but also incredibly functional, enhancing the user experience.

While there are many libraries and plugins available to add this functionality to a website, using Vanilla JavaScript offers several advantages, especially for developers who prefer lightweight, customizable, and dependency-free solutions. Vanilla JavaScript refers to using plain JavaScript, without relying on any external libraries such as jQuery or React.

In this article, we’ll walk you through the process of creating a Before After Slider using only Vanilla JavaScript.

What is a Before After Image Slider?

A Before After Image Slider is an interactive web feature that allows users to compare two images side by side by sliding a dividing line between them. This slider gives a visual representation of two different states of the same subject, such as a “before” and “after” comparison. The feature typically displays one image on the left and another on the right, with a draggable slider in between. As users drag the slider, the image on one side is revealed, while the image on the other side is hidden or partially exposed, allowing users to see the differences in the images.

How It Works:

• Before Image: This is the initial image that represents the state of something before any changes are made (for example, a “before” photo of a home renovation).
• After Image: This is the image that shows the changes, improvements, or transformations (such as the “after” photo of the same home after renovations).
• Slider Mechanism: The user interacts with the slider to move a dividing line horizontally, vertically, or diagonally. This action reveals the “before” or “after” image beneath the other, depending on the direction of the drag.

Common Use Cases for Before After Image Sliders:

• Real Estate: Showcasing property renovations, design makeovers, or different views of a property before and after a makeover.
• Beauty and Skincare: Displaying the effects of skincare products or makeup applications.
• Fitness and Health: Demonstrating the results of workouts, diet changes, or health transformations.
• E-commerce: Allowing customers to see product upgrades, design options, or different color variations.
• Photography and Art: Comparing edits or artistic alterations of photos and artwork.

Before After Image Sliders are a great way to engage users, making them interact with the content and providing a dynamic experience. The sliding feature allows users to instantly visualize the differences in images, which makes the tool valuable for numerous industries where visual comparisons are essential.

Benefits of Using a Before After Image Slider:

1. Enhanced User Engagement: Interactive elements increase user engagement and time spent on a website.
2. Clear Comparisons: A Before After Slider provides a clear, side-by-side view, making it easy to understand the difference between two images.
3. Compact and Efficient: Instead of using multiple images or complex animations, a slider condenses everything into a neat, space-efficient tool.
4. Versatility: It can be applied across various industries such as beauty, real estate, fitness, and more.

In the next section, we’ll discuss the advantages of using Vanilla JavaScript to implement a Before After Image Slider. While there are many external libraries available, using Vanilla JavaScript gives you more control over the functionality and allows you to keep your website lightweight.

Why Use Vanilla JavaScript for a Before After Image Slider?

When building web features, developers often rely on libraries like jQuery, React, or Angular for convenience. However, Vanilla JavaScript—plain JavaScript without external dependencies—offers several significant advantages, especially for a simple feature like the Before After Image Slider.

Let’s explore why you might want to choose Vanilla JavaScript for this task:

1. Lightweight and Fast Performance

One of the biggest advantages of using Vanilla JavaScript is that it doesn’t add unnecessary weight to your website. Libraries like jQuery or React can increase the overall size of your website, slowing down page load times. With Vanilla JavaScript, you’re using only the core features of the language, making the code more lightweight and efficient.

For a Before After Image Slider, performance is essential. Users expect smooth interactions when dragging the slider, and Vanilla JavaScript helps achieve that by minimizing external resources. This lightweight approach directly translates to a better user experience, especially on mobile devices where performance and loading times are even more critical.

2. No External Dependencies

By using Vanilla JavaScript, you eliminate the need for third-party libraries. This means you don’t have to worry about keeping up with updates or security vulnerabilities in external code. It also means fewer HTTP requests, which is always a plus for website performance and SEO. The more dependencies you remove from your site, the simpler and more maintainable your code becomes.

3. Full Control Over the Code

When you build features using external libraries, you’re often restricted by the options and flexibility they provide. With Vanilla JavaScript, you have complete control over how your Before After Image Slider behaves. You can customize every aspect of the slider, from the animation to the responsiveness, and make sure it aligns perfectly with your design vision.

If you’re building a feature from scratch using Vanilla JavaScript, you’re not tied to any predefined methods or frameworks. This flexibility allows you to make adjustments and add enhancements as you see fit, rather than trying to modify an external library to meet your specific needs.

4. SEO and Accessibility Benefits

Using Vanilla JavaScript can be a boon for your site’s SEO. When you load heavy JavaScript libraries, some elements might not be indexed properly by search engines, especially if they rely on client-side rendering. By keeping your website code lightweight and simple, search engines can better crawl and index the content.

In addition, using Vanilla JavaScript for interactive elements like the Before After Image Slider gives you the flexibility to ensure accessibility. You can add proper aria attributes and keyboard support without the need for third-party code that may not prioritize accessibility by default.

5. Easier Debugging and Maintenance

If you’re using a library or framework, debugging can sometimes be difficult because the source code isn’t directly in front of you. When you write your own code in Vanilla JavaScript, you have full visibility into what’s going on behind the scenes. This makes it easier to troubleshoot issues and make changes when necessary.

Additionally, maintaining Vanilla JavaScript code is often more straightforward. Since you control everything from start to finish, you don’t have to worry about conflicts between your code and external libraries, which can sometimes happen with larger projects.

6. Better Learning Opportunity

Using Vanilla JavaScript gives you a deeper understanding of how things work under the hood. As a developer, working with pure JavaScript helps strengthen your skills, making you more proficient in coding and problem-solving. It also makes it easier for you to migrate to other frameworks or libraries when needed, as you’ll have a solid foundation in the core language.

How Does a Before After Image Slider Work?

A Before After Image Slider operates based on simple but effective mechanics that enable users to compare two images interactively. The functionality behind it involves controlling the visibility of the images with a slider, typically using mouse, touch, or keyboard input. Let’s break down how the feature works:

1. Image Structure

The most essential part of the Before After Image Slider is the two images you wish to compare. These images are placed side by side, with one image typically labeled as “before” and the other as “after”. The slider divides these images and gives the user control over which part of each image is visible at any given time.

• Before Image: The first image (often the “before” state of a transformation or process).
• After Image: The second image, which represents the “after” state of the same transformation.

2. Slider Mechanism

The core interaction is the slider—a movable divider that allows the user to drag back and forth. When a user clicks and drags the slider, they reveal more of the “before” or “after” image, depending on the direction in which the slider moves. This gives users an instant and intuitive comparison between the two images.

• Horizontal or Vertical Movement: In most cases, the slider works horizontally. However, it could also function vertically or diagonally, depending on the specific use case or design of the website.
• Drag and Drop Functionality: When a user clicks on the slider, they can drag it to reveal the “before” image from the left or the “after” image from the right. The action is typically accompanied by a smooth transition or animation to enhance the visual effect.

3. Interaction Mechanics

The interaction mechanics are driven by mouse events or touch events:

• Mouse Movement: When a user clicks and holds the mouse button over the slider, they can drag it across the image container. This triggers the JavaScript logic that updates the position of the slider, making one image more visible while hiding the other.
• Touch Events (Mobile Devices): On mobile devices, the slider typically responds to touchstart, touchmove, and touchend events, enabling users to swipe the slider left or right to compare images.

4. JavaScript Logic

Behind the scenes, JavaScript handles the majority of the logic. The browser listens for user input (like mouse or touch events) and calculates the new position of the slider. The images are then dynamically adjusted based on the slider’s position, revealing more or less of each image.

For instance, when a user drags the slider to the left, JavaScript updates the CSS of the “before” image to increase its visible area, while decreasing the visibility of the “after” image. This process creates the illusion of moving from one image to the other in real time.

Step-by-Step Guide: Creating a Before After Image Slider in Vanilla JavaScript

Now that you understand the basics of how a Before After Image Slider works, let’s dive into creating your own slider using Vanilla JavaScript. We’ll go through each step, from setting up the HTML structure to adding CSS for styling and finally implementing the JavaScript to make the slider interactive.

Step 1: HTML Structure

To begin with, you’ll need a simple HTML structure. This will include two image elements: one for the “before” image and one for the “after” image. You’ll also need a slider container to hold the images and allow interaction.

Here’s a basic structure to get started:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Before After Image Slider</title>
    <link rel="stylesheet" href="styles.css">
</head>
<body>

<div class="slider-container">
    <div class="before-image">
        <img src="before.jpg" alt="Before Image">
    </div>
    <div class="after-image">
        <img src="after.jpg" alt="After Image">
    </div>
    <div class="slider" id="slider"></div>
</div>

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

Explanation of the HTML:

• slider-container: This div holds both the images and the slider itself.
• before-image & after-image: These divs contain the two images. The before-image is visible initially, while the after-image will be hidden or revealed as the slider is moved.
• slider: This is the draggable element that allows users to compare the two images by moving it left or right.

With the structure in place, we’ll move on to styling the slider and images.

Step 2: CSS Styling

Next, we need to style the slider to ensure it looks good and behaves as expected. Here’s some basic CSS to get started:

/* styles.css */
body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}

.slider-container {
    position: relative;
    width: 80%;
    max-width: 800px;
    height: 400px;
    margin: 50px auto;
    overflow: hidden;
}

.before-image,
.after-image {
    position: absolute;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    overflow: hidden;
}

.before-image img,
.after-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.slider {
    position: absolute;
    top: 0;
    left: 50%;
    width: 5px;
    height: 100%;
    background-color: #000;
    cursor: ew-resize;
    z-index: 10;
}

Explanation of the CSS:

• slider-container: This defines the container’s size and position and ensures that the images do not overflow.
• before-image & after-image: Both are set to occupy the same space, but the before-image is initially visible while the after-image is partially hidden.
• slider: Positioned in the middle of the container by default, it is styled to look like a vertical bar that users can drag to reveal or hide the images.

Now that we have the structure and styling in place, let’s move on to the interactive part using Vanilla JavaScript.

Step 3: JavaScript Logic

In this step, we’ll implement the JavaScript to make the slider interactive. The slider should move when the user clicks and drags it, revealing more or less of the “before” or “after” image.

Here’s the JavaScript code to accomplish this:

// script.js
const slider = document.getElementById('slider');
const beforeImage = document.querySelector('.before-image');
const afterImage = document.querySelector('.after-image');

let isDragging = false;

// Function to start dragging the slider
slider.addEventListener('mousedown', (e) => {
    isDragging = true;
    document.addEventListener('mousemove', moveSlider);
});

// Function to stop dragging the slider
document.addEventListener('mouseup', () => {
    isDragging = false;
    document.removeEventListener('mousemove', moveSlider);
});

// Function to move the slider and update image visibility
function moveSlider(e) {
    if (isDragging) {
        let offsetX = e.clientX - slider.getBoundingClientRect().left;
        if (offsetX < 0) offsetX = 0; // Prevent the slider from going out of bounds
        if (offsetX > slider.parentElement.offsetWidth) offsetX = slider.parentElement.offsetWidth;

        // Adjust the position of the slider
        slider.style.left = offsetX + 'px';

        // Reveal more of the after-image as the slider moves
        const widthPercent = (offsetX / slider.parentElement.offsetWidth) * 100;
        beforeImage.style.width = widthPercent + '%';
    }
}

// Make sure the initial state is correct
beforeImage.style.width = '50%';

Explanation of the JavaScript:

• mousedown Event: When the user clicks on the slider, the mousedown event is triggered. We set isDragging to true and start listening for the mousemove event to track the movement of the mouse.
• mousemove Event: This event updates the position of the slider and adjusts the width of the “before” image accordingly.
• mouseup Event: Once the user releases the mouse button, we stop tracking the mouse movement and stop adjusting the slider position.

Initially, the before image takes up 50% of the container’s width, showing half of the “before” image and half of the “after” image. As the user drags the slider, the width of the “before” image changes, revealing more of the “after” image.

Step 4: Enhancements

To make your Before After Image Slider even better, you can add several enhancements:

1. Smooth Transitions: Use CSS transitions to add a smooth sliding effect when adjusting the width of the images. Example:

   .before-image {
       transition: width 0.3s ease;
   }

2. Mobile Optimization: Ensure that the slider is touch-friendly for mobile users. We already added mouse events, but you can implement touch events like touchstart, touchmove, and touchend for a smooth mobile experience. Example:

   slider.addEventListener('touchstart', (e) => { ... });
   slider.addEventListener('touchmove', (e) => { ... });

3. Responsive Design: Make the slider container and images responsive so that they scale properly on different screen sizes. You can use media queries to adjust the layout depending on the screen width.

Best Practices for Optimizing Your Before After Image Slider

After building your Before After Image Slider using Vanilla JavaScript, it’s important to optimize it for performance, accessibility, and usability. This will ensure a smooth user experience across different devices and improve your site’s overall functionality. Here are some best practices to consider:

1. Optimize Image Sizes

Since Before After Image Sliders involve displaying two images at once, ensuring these images are optimized is essential for faster load times and better performance. Large, uncompressed images can slow down your website, especially on mobile devices.

• Image Compression: Use image compression tools like TinyPNG or ImageOptim to reduce file size without sacrificing quality.
• Responsive Images: Use different image resolutions for different screen sizes (using the srcset attribute in the <img> tag). This ensures users on mobile devices don’t load unnecessarily large images.

Example of responsive images:

<img src="before.jpg" 
     srcset="before-small.jpg 600w, before-medium.jpg 1200w, before-large.jpg 2000w" 
     alt="Before Image">

• Lazy Loading: For images that are not immediately visible on the page (for example, images in the “after” section), you can implement lazy loading so they are only loaded when the user interacts with the slider.

Example:

<img src="before.jpg" loading="lazy" alt="Before Image">

2. Improve Accessibility

Ensuring your Before After Image Slider is accessible to all users is a vital step. Here are a few tips to make your slider more inclusive:

• Keyboard Navigation: Make sure users can interact with the slider using the keyboard. For example, use the arrow keys to move the slider left and right.

Example (JavaScript for keyboard support):

document.addEventListener('keydown', (e) => {
    if (e.key === 'ArrowLeft') {
        moveSliderLeft();
    } else if (e.key === 'ArrowRight') {
        moveSliderRight();
    }
});

• Aria Labels and Descriptions: Use ARIA (Accessible Rich Internet Applications) attributes to provide a better experience for users with screen readers. Add appropriate labels to the slider so that screen readers can announce it properly.

Example:

<div class="slider" id="slider" aria-label="Before and After Image Slider" role="slider" aria-valuemin="0" aria-valuemax="100" aria-valuenow="50">
</div>

• Descriptive Alt Text: Ensure that the images used in the slider have descriptive alt text for visually impaired users.

Example:

<img src="before.jpg" alt="Before renovation showing an old kitchen">
<img src="after.jpg" alt="After renovation showing a modern kitchen">

3. Enhance the Visual Appeal

While functionality is essential, making your Before After Image Slider visually appealing can further improve user engagement. Here are some ideas to make the slider more attractive:

• Smooth Animations: As mentioned earlier, you can use CSS transitions to make the image sliding smoother. This helps create a more polished experience.

Example of smooth transition:

.before-image {
    transition: width 0.4s ease;
}

• Slider Styling: Customize the appearance of the slider handle. You can change its color, add hover effects, or make it visually distinctive to enhance the overall look.

Example:

.slider {
    width: 10px;
    background-color: #007bff;
    border-radius: 5px;
}
.slider:hover {
    background-color: #0056b3;
}

• Custom Cursor: Change the cursor style when users hover over the slider to make the interaction more intuitive.

Example:

.slider {
    cursor: ew-resize; /* Change the cursor to indicate horizontal resizing */
}

4. Ensure Responsiveness

Since users access websites from various devices, your Before After Image Slider needs to be responsive. Here’s how to ensure it works well on different screen sizes:

• Responsive Layout: Use media queries to adjust the layout of the slider for smaller screens. You may need to adjust the width of the container and slider for mobile users.

Example of media query for mobile:

@media (max-width: 600px) {
    .slider-container {
        width: 100%;
        height: 300px;
    }
}

• Mobile Touch Support: As mentioned earlier, it’s important to ensure the slider works smoothly on mobile devices. This means implementing touch events like touchstart, touchmove, and touchend to allow swiping functionality on mobile screens.

Example:

slider.addEventListener('touchstart', (e) => {
    isDragging = true;
    document.addEventListener('touchmove', moveSlider);
});

slider.addEventListener('touchend', () => {
    isDragging = false;
    document.removeEventListener('touchmove', moveSlider);
});

5. Test Across Multiple Browsers and Devices

After building the Before After Image Slider, ensure you test it across various browsers and devices to guarantee compatibility. Although modern browsers generally support JavaScript and CSS transitions, it’s always a good practice to test on:

• Different browsers (Chrome, Firefox, Safari, Edge, etc.)
• Mobile devices (iPhone, Android, tablets)
• Various screen sizes (desktop, tablet, and mobile)

Testing ensures that your slider performs well for all users, providing them with the best possible experience.

Frequently Asked Questions (FAQs)

Here are some common questions related to creating and using a Before After Image Slider in Vanilla JavaScript, along with helpful answers:

1. Can I use the Before After Image Slider with more than two images?

While the classic Before After Image Slider is designed for two images, it is possible to extend this functionality to compare more than two images. To do this, you would need to modify the logic of the slider to handle multiple layers of images and adjust the visibility of each one based on the slider’s position.

This would involve:

• Placing multiple images within the container.
• Updating the slider movement logic to control the visibility of each image as the slider moves.
• Possibly creating additional sliders or controls to switch between image sets.

2. How can I add captions or labels to the Before After Image Slider?

Adding captions or labels to the Before After Image Slider can be done by positioning them over or below the images. To keep the slider design clean, you can use position: absolute to overlay text on top of the images.

Example of adding a caption:

<div class="slider-container">
    <div class="before-image">
        <img src="before.jpg" alt="Before Image">
        <div class="caption">Before</div>
    </div>
    <div class="after-image">
        <img src="after.jpg" alt="After Image">
        <div class="caption">After</div>
    </div>
    <div class="slider" id="slider"></div>
</div>

CSS for caption:

.caption {
    position: absolute;
    bottom: 10px;
    left: 50%;
    transform: translateX(-50%);
    background-color: rgba(0, 0, 0, 0.5);
    color: #fff;
    padding: 5px 10px;
    font-size: 16px;
}

This will display the text “Before” and “After” at the bottom of the respective images. You can adjust the positioning and styles according to your design needs.

3. How can I prevent the slider from going out of bounds?

In the JavaScript code provided earlier, there is logic that ensures the slider stays within the bounds of the container. However, it’s important to handle edge cases to ensure the slider cannot be dragged too far left or right, beyond the container’s width.

In the moveSlider function, ensure that the slider’s position is restricted within the container’s width:

if (offsetX < 0) offsetX = 0;  // Prevent slider from going left
if (offsetX > slider.parentElement.offsetWidth) offsetX = slider.parentElement.offsetWidth;  // Prevent slider from going right

This will ensure the slider does not exceed the boundaries and remain within the container, providing a seamless experience for the user.

4. Can I customize the slider’s appearance?

Yes! The appearance of the slider can be easily customized using CSS. You can change the slider’s width, height, background color, and even add hover effects.

Example of customizing the slider:

.slider {
    position: absolute;
    top: 0;
    left: 50%;
    width: 12px;
    height: 100%;
    background-color: #3498db;
    border-radius: 8px;
    cursor: ew-resize;
    z-index: 10;
    transition: background-color 0.3s ease;
}

.slider:hover {
    background-color: #2ecc71;  /* Change color on hover */
}

This will make the slider thicker and change its color on hover. You can modify other properties, like adding shadows or borders, to fit your design.

5. How can I make the Before After Image Slider work on mobile devices?

To make the slider work smoothly on mobile devices, you need to ensure it supports touch events. You can use the same logic as mouse events but adapted for touch events. Here’s how you can add touch support:

Example of adding touch support:

slider.addEventListener('touchstart', (e) => {
    isDragging = true;
    document.addEventListener('touchmove', moveSlider);
});

slider.addEventListener('touchend', () => {
    isDragging = false;
    document.removeEventListener('touchmove', moveSlider);
});

Additionally, ensure that the slider is sized appropriately for smaller screens using responsive design principles. Media queries in your CSS can help you adjust the slider’s appearance on different screen sizes, making it mobile-friendly.

Example of responsive design for mobile:

@media (max-width: 768px) {
    .slider-container {
        width: 100%;
        height: 300px;
    }
    .slider {
        width: 8px;  /* Smaller slider for mobile */
    }
}

This ensures that the slider looks good and functions properly on all devices.

6. Can I add a smooth animation when dragging the slider?

Yes! You can use CSS transitions to add a smooth animation when the slider is moved. This is particularly useful for a more polished user experience.

For instance, you can add a transition effect to the .before-image so that the width adjustment happens smoothly:

.before-image {
    transition: width 0.3s ease-in-out;
}

This will create a smooth transition effect when dragging the slider to reveal more or less of the before image.

7. How do I handle different screen resolutions?

Handling different screen resolutions requires ensuring that both your images and slider are responsive. You can achieve this by using responsive images and flexible layouts.

• Use srcset to provide different image resolutions based on the user’s screen size.
• Make the container and images flexible by using percentage-based widths instead of fixed pixel values.

Conclusion

The Before After Image Slider is a powerful and engaging feature for websites, allowing users to compare images interactively. By using Vanilla JavaScript, you can create a lightweight, customizable, and fast solution without relying on third-party libraries. We’ve covered everything from building the basic slider to optimizing it for performance, accessibility, and responsiveness.

By following the step-by-step guide, applying best practices, and considering the frequently asked questions, you’ll be able to implement a fully functional Before After Image Slider that enhances the user experience on your website.