Tutorial - Create a Carousel with JavaScript

Tutorial - Create a Carousel with JavaScript
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JavaScript Carousel

In this tutorial you will learn how to create a simple Carousel like the one below.

tutorial 2 gif

We will only use HTML and CSS and a bit of JavaScript.

If you want to learn more about JavaScript, check out my book, available for purchase on Amazon

Before we start creating the structure of our carousel, go ahead and paste this code in the head of your html file:

    <link  href="https://fonts.googleapis.com/css?family=Roboto:400,700"  rel="stylesheet">

We will use Roboto as the font for our project.  

Creating the HTML structure for the Carousel

For the structure of the Carousel we won't need many elements:

  • a container
  • a wrapper for each slide
  • 3 different slides
    <div class="container">
            <div class="row">
                <h1>Testimonials</h1>
                <div id="slider">
                    <div class="button-left slider-button">
                        <span> < </span> 
                    </div> 
                    <div class="button-right slider-button">
                        <span> > </span>
                    </div>
                    <div class="slide slide1 showing">
                        <div class="slide-text">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed consectetur
                            ullamcorper convallis. Suspendisse quis
                            imperdiet nisi, et accumsan enim. Donec tempus mi ex, ac.</div>
                        <div class="slide-testimonial">
                            <div class="slide-img"><img alt="testimonial" src="./images/testimonial1.jpg"></div>
                            <div class="slide-person">
                                <p>Jane Doe</p>
                                <p>CEO Company x</p>
                            </div>
                        </div>
                    </div>
                  </div>
            </div>
        </div>

this will be the structure of our carousel As you can see I've only pasted the code for the first slide, go ahead and add two more, choosing a picture and a description that you like.  

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Styling the Carousel with CSS

Let's start styling the carousel. Paste this code to apply some basic style to the body and the wrapper for the carousel:

    :root {
        /* we define some variables to hold our colors*/
        --bg-section: #374057;
        --color-headers: #2c3e50;
        --color-highlight-green: #00AF4E;
        --color-light-gray: #EEEFF2;
    }

    * {
        /* apply our google font */
        font-family: 'Roboto', sans-serif;
        padding: 0;
        margin: 0;
        text-decoration: none;
        font-size: 16px;
    }

    body {
        /* make the body full height */
        position: relative;
        height: 100vh;
        background-color: var(--bg-section);
        display: flex;
    }

    /* position our container in the middle */
    .container {
        width: 900px;
        margin: auto;
        padding: 20px;
    }

    /* style the header */
    h1 {
        font-size: 2rem;
        color: white;
        text-align: center;
    }

Awesome, now it's time to move on to the actual carousel.

    /*create slider */
    #slider {
        position: relative;
        height: 300px;
        padding: 0;
        margin: 0;
        margin-top: 30px;
        margin-bottom: 30px;
    }

    .slide {
        /* we position the slide absolutely compared to its parent #slider */
        position: absolute;
        left: 0px;
        top: 0px;
        width: 100%;
        height: 100%;
        opacity: 0;
        z-index: 1;
        /* change the value for a faster or slower transition between slides */
        -webkit-transition: opacity 0.5s;
        -o-transition: opacity 0.5s;
        transition: opacity 0.5s;
    }

    /* class to show the current slide */
    .showing {
        opacity: 1;
        z-index: 2;
    }

    .slide-text {
        background-color: white;
        border-radius: 10px;
        margin: auto;
        padding: 40px;
        padding-left: 60px;
        position: relative;
    }

    /* create the notch */
    .slide-text:after {
        content: '';
        display: block;
        position: absolute;
        bottom: -20px;
        left: calc(50%);
        -webkit-transform: translateX(-50%);
        -ms-transform: translateX(-50%);
        transform: translateX(-50%);
        width: 0;
        height: 0;
        border-style: solid;
        border-width: 20px 26px 0 0;
        border-color: white transparent transparent transparent;
    }

    /* align the testimonial in the center */
    .slide-testimonial {
        margin-top: 20px;
        display: -webkit-box;
        display: -ms-flexbox;
        display: flex;
        -webkit-box-pack: center;
        -ms-flex-pack: center;
        justify-content: center;
        -webkit-box-align: center;
        -ms-flex-align: center;
        align-items: center;
    }

    .slide-img {
        margin: 10px;
    }

    .slide-img img {
         width: 100px;
        height: 100px; 
        border-radius: 50%;
        border: 4px solid white;
    }

    .slide-person {
        margin-left: 20px;
    }

    .slide-person p {
        padding: 5px;
    }

    /* make the name of the person bold */
    .slide-person p:first-of-type {
        color: white;
        font-weight: bold;
        font-size: 1.2rem;
    }

    /* make their job title light gray */
    .slide-person p:last-of-type {
        color: var(--color-light-gray);
    }

    /* position the buttons and make them green */
    .slider-button {
        cursor: pointer;
        color: white;
        font-weight: bold;
        width: 40px;
        height: 40px;
        background-color: var(--color-highlight-green);
        z-index: 3;
        position: absolute;
        text-align: center;
        border-radius: 20%;
        -webkit-box-shadow: 0 8px 16px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
        box-shadow: 0 8px 16px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
        display: -webkit-box;
        display: -ms-flexbox;
        display: flex;
        -webkit-box-pack: center;
        -ms-flex-pack: center;
        justify-content: center;
        -webkit-box-align: center;
        -ms-flex-align: center;
        align-items: center;
    }

    /*posion the left an right button horizontally */
    .button-left {
        position: absolute;
        left: -10px;
    }

    .button-right {
        position: absolute;
        right: -10px;
    }

We applied some simple styling and made use of flexbox to create the layout we wanted. If you are wondering why I repeated some styles such as:

    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;

This is called prefixing, and it is used to ensure that our css will work on every browser. You can use something like Autoprefixer to prefix your code and be sure that no matter what browser your users will use, they will experience your app/website the way you intended.  

Make the Carousel work with JavaScript

Right now our slider is not working, we need to write some JavaScript to be able to change slide when pressing a button. Copy this code in your script.js file

    document.addEventListener("DOMContentLoaded", () => {

        // grab all the slides 
        let slides = document.querySelectorAll("#slider .slide");
        // set initial slide
        let currentSlide = 0;
        //grab both buttons
        const nextButton = document.querySelector(".button-right");
        const prevButton = document.querySelector(".button-left");

        function nextSlide() {
            // current slide becomes hidden
            slides[currentSlide].className = 'slide';
            // set the current slide as the next one
            currentSlide = (currentSlide + 1) % slides.length;
            // add the class showing to the slide to make it visible
            slides[currentSlide].className = 'slide showing';
        }

        function prevSlide() {
             // current slide becomes hidden
            slides[currentSlide].className = 'slide';
            // set the current slide as the previous one
            currentSlide = (currentSlide - 1) % slides.length;
            
            if (currentSlide == -1) { 
                currentSlide = slides.length-1; 
            } 
            // add the class showing to the slide to make it visible
            slides[currentSlide].className = 'slide showing';
        }

        nextButton.addEventListener("click", () => {
            // go to next slide on click of the button
            nextSlide();
        });
        prevButton.addEventListener("click", () => {
            // go to previous slide on click of the button
            prevSlide();
        });

        /* VERTICALLY ALIGN THE BUTTONS IN THE MIDDLE OF THE SLIDER TEXT
         */
        function positionSliderButton() {
            // grab the slider
            let slider = document.querySelector('.slide-text');
            // grab its height
            let sliderHeight = slider.getBoundingClientRect().height;
            // grab the button
            let buttons = document.querySelectorAll('.slider-button');

            // for each of the buttons
            for (button of buttons) {
                // get their height
                let buttonHeight = button.getBoundingClientRect().height;
                // position them right in the middle of the text,
                button.style.top = (((sliderHeight - buttonHeight) / 2).toString()) + "px";
            }
        }
        positionSliderButton();

        // whenever the window is resize, reposition the buttons
        window.addEventListener('resize', () => {
            positionSliderButton();
        });

    });

What we are doing is very simple:

  • we grab an array of our slides
  • we toggle a class that will be used to make a slide visible
  • if the user presses the next button, we apply that class to the next slide
  • conversely if they press the previous button, we apply it to the previous slide

The second part of the code is used to ensure that our buttons are always positioned in the middle of the text of the slide. I wanted to do it this way to show you a cool property: button.getBoundingClientRect().height; that we used to grab the height of the button. I have used window.addEventListener('resize', () => { positionSliderButton(); }); to make sure that whenever a user resizes the page, the button will move to stay in the correct position


Thank you very much for reading. Follow me on DevTo or on Twitter for more.

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Alberto is a software developer specialized in building enterpise software using Angular and author of the 'Complete guide to Modern JavaScript' ebook and course. In his free time he writes articles and tutorials on InspiredWebDev.com and Dev.to

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