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HTML

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Adding Classes

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About the <head>

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CSS

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CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <header>
	<h1>Accessible <code style="white-space:nowrap;">&lt;image-compare&gt;</code> <span>Web Component</span> <small>(no Shadow DOM)</small></h1>
	<ul>
		<li>Using Light DOM allows you to style everything with regular CSS</li>
		<li>Horizontally scrollable container used as fallback if JS doesn't load (this also helps reduce CLS by stabilizing the overall height)</li>
		<li>No dependencies</li>
		<li><a href="https://github.com/nonsalant/image-compare" target="_parent">View on Github</a> (code organized into separate files)</li>
	</ul>
	<hr>
	<blockquote>
		Control how much of the first image is shown initially by adding an exposure attribute (0-100).
		<br>
		<small>
			<i>E.g:</i> <code style="font-size:1.2em;">&lt;image-compare <b>exposure="0"</b>&gt;</code> will hide the first image, a value of 100 will hide the second image, and a value of 50 will show half of each.
		</small>
	</blockquote>
	<hr>
</header>

<h2>Example 1: Just two <code>&lt;img&gt;</code> tags</h2>

<image-compare>
	<img alt="Alt text" src="https://assets.codepen.io/8247/Screenshot+2024-12-26+at+04.11.10.jpg" width="3584" height="2240" />
	<img alt="Alt text" src="https://assets.codepen.io/8247/Screenshot+2024-12-26+at+04.11.01.jpg" width="3584" height="2240" />
</image-compare>

<h2>Example 2: With a caption &amp; wrapped in a <code>&lt;figure&gt;</code></h2>

<figure>
	<image-compare>
		<img alt="Alt text" src="https://images.unsplash.com/photo-1548840566-8179dfe68157?crop=entropy&cs=srgb&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE3MzQ5MTE0Mjd8&ixlib=rb-4.0.3&q=85" />
		<img alt="Alt text" src="https://images.unsplash.com/photo-1646174050199-f6f9b32bd2f7?crop=entropy&cs=srgb&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE3MzQ5MTE0Mjd8&ixlib=rb-4.0.3&q=85" />
	</image-compare>
	<figcaption>Before/After</figcaption>
</figure>

<footer>
	<div style="display: flex; align-items: center; gap: 1rem; border: dotted 1px; margin-block: 1.5rem; padding: .5rem 1rem;">
		<h5 style="text-align: center; min-width: fit-content;">Too much CSS?</h5>
		<p><a href="https://codepen.io/nonsalant/pen/pvzrzdM" target="_parent" title="Opens in the parent frame" style="text-decoration:underline">Try this version</a> where non-critical CSS is moved to JS and made more DRY.</p>
	</div>
	<ul>
		<li>Forked from: <a target="_blank" href="https://cloudfour.com/thinks/building-an-accessible-image-comparison-web-component/">image-compare</a> by Paul Hebert for Cloud Four, which <a href="https://github.com/cloudfour/image-compare/blob/main/src/index.js" target="_blank">uses the Shadow DOM</a>.
		</li>
		<li>Inspired by this article: <a target="_blank" href="https://frontendmasters.com/blog/light-dom-only/#you-can-augment-or-replace-the-html-with-whatever">Light-DOM-Only Web Components are Sweet</a> by Chris Coyier.</li>
	</ul>
</footer>
!

CSS 

              
                /* Remove default margin if nested in a figure */
figure:has(image-compare) { margin-inline: 0; }

image-compare {
	& {
		--exposure: 50%;
		--thumb-background-color: hsla(0, 0%, 100%, 0.9);
		--thumb-background-image: url('data:image/svg+xml;utf8,<svg viewbox="0 0 60 60" width="60" height="60" xmlns="http://www.w3.org/2000/svg"><path fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="4" d="M20 20 L10 30 L20 40"/><path fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="4" d="M40 20 L50 30 L40 40"/></svg>');
		--thumb-size: clamp(3em, 10vmin, 5em);
		--thumb-radius: 50%;
		--thumb-border-color: hsla(0, 0%, 0%, 0.9);
		--thumb-border-size: 2px;
		--focus-width: var(--thumb-border-size);
		--focus-color: hsl(200, 100%, 80%);
		--divider-width: 2px;
		--divider-color: hsla(0, 0%, 0%, 0.9);
	}
	& {
		position: relative;
		display: flex;
		width: fit-content;
		max-width: 100%;
		margin-inline: auto;
		img { width: 100%; height: auto; }
		label {
			position: absolute;
			inset: 0;
			display: flex;
			align-items: stretch;
		}
		[type=range] {
			cursor: col-resize;
			appearance: none;
			-webkit-appearance: none;
			background: none;
			border: none;
			margin: 0 calc(var(--thumb-size) / -2);
			width: calc(100% + var(--thumb-size));
			height: unset;
		}
		/* Styling range inputs requires separately defining the CSS rules for -moz and -webkit. */
		/* ! bug in Safari when trying to nest -moz and -webkit together under the same [type=range] */
		[type=range] {
			&::-moz-range-track { height: unset; background: transparent; }
			&::-moz-range-thumb {
				background-color: var(--thumb-background-color);
				background-image: var(--thumb-background-image);
				background-size: 90%;
				background-position: center center;
				background-repeat: no-repeat;
				border-radius: var(--thumb-radius);
				border: var(--thumb-border-size) var(--thumb-border-color) solid;
				color: var(--thumb-border-color);
				width: var(--thumb-size);
				height: var(--thumb-size);
				margin: 0;
			}
			&:focus::-moz-range-thumb { box-shadow: 0px 0px 0px var(--focus-width) var(--focus-color); }
		}
		[type=range] {
			&::-webkit-slider-runnable-track { height: unset; background: transparent; }
			&::-webkit-slider-thumb {
				-webkit-appearance: none;
				background-color: var(--thumb-background-color);
				background-image: var(--thumb-background-image);
				background-size: 90%;
				background-position: center center;
				background-repeat: no-repeat;
				border-radius: var(--thumb-radius);
				border: var(--thumb-border-size) var(--thumb-border-color) solid;
				color: var(--thumb-border-color);
				width: var(--thumb-size);
				height: var(--thumb-size);
				margin: 0;
			}
			&:focus::-webkit-slider-thumb { box-shadow: 0px 0px 0px var(--focus-width) var(--focus-color); }
		}
	}
	&:not(:defined) {
		flex-direction: row;
		overflow-x: auto;
	}
	&:defined {
		flex-direction: column;
		overflow: clip;
		.image-2-wrapper {
			position: absolute;
			top: 0;
			/* shadow used for vertiacal divider */
			filter: drop-shadow( calc(-1*var(--divider-width)) 0 0 var(--divider-color) );
			img {
				--_top-left: calc(var(--exposure) + var(--divider-width)/2);
				--_bottom-left: calc(var(--exposure) + var(--divider-width)/2);
				clip-path: polygon(var(--_top-left) 0, 100% 0, 100% 100%, var(--_bottom-left) 100%);
			}
		}
	}
	/* adjecent figcaption */
	& + figcaption { 
		text-align: center; 
		margin-block-start: .5lh; 
	}
	/* utils */
	.visually-hidden {
		position: absolute;
		width: 1px; height: 1px;
		padding: 0; margin: -1px;
		overflow: hidden;
		clip: rect(0, 0, 0, 0);
		white-space: nowrap; /* added line */
		border: 0;
	}
}

/* You probably don't need the styles below */
@layer reset {
	*, *:before, *:after { box-sizing: border-box; }
/* 	img { display: block; max-width: 100%; height: auto; } */
}
@layer demo {
	html { color-scheme: light dark; }
	body {
		font-family: system-ui;
		font-family: 'SF Pro Text', 'SF Pro Icons', 'AOS Icons', 'Helvetica Neue', Helvetica, Arial, sans-serif, system-ui;
		text-wrap: balance;
		text-wrap: pretty;
		line-height: 1.4;
		padding-inline: 1lh;
		max-width: 45rem;
		margin-inline: auto;
	}
	a {
		color: inherit; font-weight: bold;
		text-decoration: none;
		&:hover { text-decoration: underline; }
	}
}
!

JS 

              
                class ImageCompare extends HTMLElement {
	
	defaultExposure = 50;
	exposure = this.getAttribute('exposure') || this.defaultExposure;
	inputSelector = 'input[type=range]';
	secondImg = this.querySelectorAll('img')[1];
	
	/**
	* Generates an HTML string for a `<label>` containing a visually hidden
	* description for screen readers and an `<input type="range">` slider 
	* for setting the exposure value.
	*/
	ui(exposure) { 
		return `
		<label>
			<span class="visually-hidden">
				Control how much of each overlapping image is shown.
				0 means the first image is completely hidden.
				100 means the first image is fully visible.
				50 means both images are half-shown, half-hidden.
			</span>
			<input type="range" value="${exposure}" min="0" max="100" />
		</label>`;
	}
	
	constructor() { super(); }

	connectedCallback() {
		// setTimeout(() => {
			this.#setPropPercentage('--exposure', this.defaultExposure);
			this.#wrapSecondImg('span', 'image-2-wrapper');
			this.#appendHtml(this.ui(this.exposure));
			this.#setupInputListener(this.inputSelector);
		// });
	}

	static get observedAttributes() { return ['exposure']; }

	attributeChangedCallback(name, oldValue, newValue) {
		if (name === 'exposure') {
				const rangeInput = this.querySelector(this.inputSelector);
				if (rangeInput) {
						rangeInput.value = newValue;
						this.#setPropPercentage('--exposure', newValue);
				}
		}
	}

	#setupInputListener(el) {
		const rangeInput = this.querySelector(el);
		const handleInputChange = () => {
			this.setAttribute('exposure', rangeInput.value);
		};
		rangeInput.addEventListener('input', handleInputChange);
		rangeInput.addEventListener('change', handleInputChange);
	}

	#appendHtml(rawHtml) {
		const tempDiv = document.createElement('div');
		tempDiv.innerHTML = rawHtml;
		while (tempDiv.firstChild) {
			this.appendChild(tempDiv.firstChild);
		}
	}
	
	#wrapSecondImg(tag, className) {
		this.wrap(this.secondImg, tag, className);
	}
	
	#setPropPercentage(prop, value) {
		this.style.setProperty(prop, value + '%');
	}
	
	wrap(el, tag, className) {
		const wrapper = Object.assign(
			document.createElement(tag), {
				className: className
			}
		);
		el.parentNode.insertBefore(wrapper, el);
		wrapper.appendChild(el);
	}
	
}

customElements.define('image-compare', ImageCompare);
!
999px

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