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Learn to build an accessible image slider in JavaScript with keyboard navigation, auto-advance, fade transitions, caption overlay, and fullscreen mode.
What You'll Learn
- How to manage a current index and switch images
- How to implement fade transitions via CSS class toggling
- How to add captions that update with each image
- How to support keyboard navigation (ArrowLeft / ArrowRight)
- How to use the Fullscreen API for an immersive view
Project Overview
An image slider is simpler than a carousel — it shows one image at a time with a smooth crossfade and a caption. It's great for portfolios, product photography, or any content gallery.
Component Structure
How It Works — Flow Diagram
text example
goTo(index)
→ fade out current image (opacity: 0)
→ after 300ms: swap src, update caption, counter
→ fade in new image (opacity: 1)
Auto-play
→ setInterval(goNext, 4000)
→ pauses on mouseover / focus
Keyboard
→ ArrowLeft → goPrev()
→ ArrowRight → goNext()
→ "f" → toggleFullscreen()Step-by-Step Build
Step 1 — Image Data
Example
const slides = [
{ src: "img/mountain.jpg", caption: "Sunrise over the Rockies" },
{ src: "img/ocean.jpg", caption: "Pacific Ocean at dusk" },
{ src: "img/forest.jpg", caption: "Old-growth redwood forest" },
{ src: "img/city.jpg", caption: "New York City by night" },
{ src: "img/desert.jpg", caption: "Sahara sand dunes" },
];
let current = 0;
let timer = null;
const DELAY = 4000;
Step 2 — HTML Structure
html example
<div class="slider" id="slider">
<figure class="slider-frame">
<img id="sliderImg" src="" alt="" class="slider-img active">
<figcaption id="caption" class="caption"></figcaption>
</figure>
<button id="prevBtn" class="nav-btn nav-prev" aria-label="Previous">‹</button>
<button id="nextBtn" class="nav-btn nav-next" aria-label="Next">›</button>
<div id="counter" class="counter"></div>
<div class="controls">
<button id="fsBtn" class="ctrl-btn">⛶ Fullscreen</button>
<button id="pauseBtn" class="ctrl-btn">⏸ Pause</button>
</div>
</div>Step 3 — GoTo with Crossfade
Example
const img = document.getElementById("sliderImg");
const caption = document.getElementById("caption");
const counter = document.getElementById("counter");
function goTo(index) {
current = ((index % slides.length) + slides.length) % slides.length;
img.classList.remove("active"); // fade out
setTimeout(() => {
img.src = slides[current].src;
img.alt = slides[current].caption;
caption.textContent = slides[current].caption;
counter.textContent = `${current + 1} / ${slides.length}`;
img.classList.add("active"); // fade in
}, 300);
}
function goNext() { goTo(current + 1); }
function goPrev() { goTo(current - 1); }
Step 4 — CSS for Fade
css example
.slider-img {
opacity: 0;
transition: opacity 0.3s ease;
}
.slider-img.active {
opacity: 1;
}Step 5 — Navigation Buttons
Example
document.getElementById("prevBtn").addEventListener("click", () => { goPrev(); resetTimer(); });
document.getElementById("nextBtn").addEventListener("click", () => { goNext(); resetTimer(); });
Step 6 — Auto-Play
Example
function startTimer() { timer = setInterval(goNext, DELAY); }
function stopTimer() { clearInterval(timer); }
function resetTimer() { stopTimer(); startTimer(); }
const pauseBtn = document.getElementById("pauseBtn");
let paused = false;
pauseBtn.addEventListener("click", () => {
paused = !paused;
paused ? stopTimer() : startTimer();
pauseBtn.textContent = paused ? "▶ Play" : "⏸ Pause";
});
Step 7 — Keyboard Navigation
Example
document.addEventListener("keydown", (e) => {
if (e.key === "ArrowLeft") { goPrev(); resetTimer(); }
if (e.key === "ArrowRight") { goNext(); resetTimer(); }
if (e.key === "f" || e.key === "F") toggleFullscreen();
});
Step 8 — Fullscreen API
Example
function toggleFullscreen() {
const slider = document.getElementById("slider");
if (!document.fullscreenElement) {
slider.requestFullscreen().catch(err => console.warn("Fullscreen error:", err));
} else {
document.exitFullscreen();
}
}
document.getElementById("fsBtn").addEventListener("click", toggleFullscreen);
Step 9 — Initialize
js example
goTo(0);
startTimer();Console Output
Output
goTo(0) → img.src = "img/mountain.jpg" → caption = "Sunrise over the Rockies" → counter = "1 / 5" --- 4 seconds pass --- goTo(1) → img fade out → src = "img/ocean.jpg" → fade in → caption = "Pacific Ocean at dusk" → counter = "2 / 5" --- User presses ArrowLeft --- goTo(0) → wrapped to: counter = "1 / 5" --- User presses "f" --- slider.requestFullscreen() → browser enters fullscreen
Edge Cases to Handle
| Situation | Expected Behavior |
|---|---|
| Wrap around (last → next) | Index wraps to 0 |
| Wrap around (first → prev) | Index wraps to last |
| Fullscreen not supported | catch() silently handles |
| Rapid clicks | 300ms fade completes before next swap |
| Single image | Hide prev/next buttons |
Challenge Yourself
- Thumbnail strip — show small clickable thumbnails below the slider
- Progress bar — animate a thin bar that fills during the auto-advance delay
- Lazy loading — only load images as they become active
- Zoom on hover — scale the image slightly when the mouse enters
- Share slide — add a copy-URL button that links directly to the current slide
Best Practices
- Use
setTimeoutinsidegoTo()for the crossfade delay, notsetInterval - Always use safe wrap-around:
((index % len) + len) % len - Apply CSS
transitionon the element, not JavaScript animations - Provide
aria-labelon all navigation buttons for accessibility - Pause auto-play when the user is actively interacting
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Build a JavaScript Image Slider - Step by Step Project Tutorial.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this JavaScript Master Course topic.
Search Terms
javascript-complete-guide, javascript master course, javascript, complete, guide, mini, projects, image
Related JavaScript Master Course Topics
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