kevnk/alpinejs-parallax.js

## alpinejs-parallax.js
/**
 * Installation and setup:
 * 0. Install AlpineJS: `npm i -S alpinejs`
 * 1. Make sure AlpineJS is running by adding `x-data` attribute on opening `<body>` tag
 * 2. Add `x-parallax="path/to/image.jpg"` on element to add parallax bg image
 *
 * PS. this code was partially generated from ChatGPT 4
 */

// Helper function to load an image and return its natural dimensions
const loadImage = async (src) => {
    return new Promise((resolve, reject) => {
        const img = new Image();
        img.onload = () => resolve({ width: img.naturalWidth, height: img.naturalHeight });
        img.onerror = () => reject(new Error('Failed to load image'));
        img.src = src;
    });
};

Alpine.directive('parallax', (el, { expression }, { effect, cleanup }) => {
    const src = expression;

    // Set initial styles for the element
    el.style.backgroundImage = `url(${src})`;
    el.style.backgroundAttachment = 'fixed';
    el.style.backgroundPosition = 'center';
    el.style.backgroundRepeat = 'no-repeat';

    // Function to handle scroll event
    const scrollSpeed = 0.5; // Adjust this value to change the parallax speed (0.5 means 50% slower than scroll)
    const onScroll = () => {
        const yPos = -(window.scrollY - el.offsetTop) * scrollSpeed;
        el.style.backgroundPosition = `center ${yPos}px`;
    };

    onScroll();

    const onResize = async () => {
        const windowHeight = window.innerHeight;
        const windowWidth = window.innerWidth;
        const extraHeight = windowHeight * scrollSpeed; // Calculate extra height needed for the parallax effect

        try {
            // Load image and get natural dimensions
            const { width: naturalWidth, height: naturalHeight } = await loadImage(src);

            // Calculate aspect ratio and target dimensions
            const aspectRatio = naturalWidth / naturalHeight;
            let targetHeight = windowHeight + extraHeight;
            let targetWidth = targetHeight * aspectRatio;

            // If the target width is less than the window width, adjust the dimensions
            if (targetWidth < windowWidth) {
                targetWidth = windowWidth;
                targetHeight = targetWidth / aspectRatio;
            }

            el.style.backgroundSize = `${targetWidth}px ${targetHeight}px`;
        } catch (error) {
            console.error('Error:', error.message);
        }
    };

    // Add event listeners and run effects
    effect(() => {
        onResize(); // Set initial background size
        window.addEventListener('resize', onResize);
        window.addEventListener('scroll', onScroll);
    });

    // Clean up when directive is removed or the element is removed from the DOM
    cleanup(() => {
        window.removeEventListener('resize', onResize);
        window.removeEventListener('scroll', onScroll);
    });
});

Alpine.start();
	/**
	* Installation and setup:
	* 0. Install AlpineJS: `npm i -S alpinejs`
	* 1. Make sure AlpineJS is running by adding `x-data` attribute on opening `<body>` tag
	* 2. Add `x-parallax="path/to/image.jpg"` on element to add parallax bg image
	*
	* PS. this code was partially generated from ChatGPT 4
	*/

	// Helper function to load an image and return its natural dimensions
	const loadImage = async (src) => {
	return new Promise((resolve, reject) => {
	const img = new Image();
	img.onload = () => resolve({ width: img.naturalWidth, height: img.naturalHeight });
	img.onerror = () => reject(new Error('Failed to load image'));
	img.src = src;
	});
	};

	Alpine.directive('parallax', (el, { expression }, { effect, cleanup }) => {
	const src = expression;

	// Set initial styles for the element
	el.style.backgroundImage = `url(${src})`;
	el.style.backgroundAttachment = 'fixed';
	el.style.backgroundPosition = 'center';
	el.style.backgroundRepeat = 'no-repeat';

	// Function to handle scroll event
	const scrollSpeed = 0.5; // Adjust this value to change the parallax speed (0.5 means 50% slower than scroll)
	const onScroll = () => {
	const yPos = -(window.scrollY - el.offsetTop) * scrollSpeed;
	el.style.backgroundPosition = `center ${yPos}px`;
	};

	onScroll();

	const onResize = async () => {
	const windowHeight = window.innerHeight;
	const windowWidth = window.innerWidth;
	const extraHeight = windowHeight * scrollSpeed; // Calculate extra height needed for the parallax effect

	try {
	// Load image and get natural dimensions
	const { width: naturalWidth, height: naturalHeight } = await loadImage(src);

	// Calculate aspect ratio and target dimensions
	const aspectRatio = naturalWidth / naturalHeight;
	let targetHeight = windowHeight + extraHeight;
	let targetWidth = targetHeight * aspectRatio;

	// If the target width is less than the window width, adjust the dimensions
	if (targetWidth < windowWidth) {
	targetWidth = windowWidth;
	targetHeight = targetWidth / aspectRatio;
	}

	el.style.backgroundSize = `${targetWidth}px ${targetHeight}px`;
	} catch (error) {
	console.error('Error:', error.message);
	}
	};

	// Add event listeners and run effects
	effect(() => {
	onResize(); // Set initial background size
	window.addEventListener('resize', onResize);
	window.addEventListener('scroll', onScroll);
	});

	// Clean up when directive is removed or the element is removed from the DOM
	cleanup(() => {
	window.removeEventListener('resize', onResize);
	window.removeEventListener('scroll', onScroll);
	});
	});

	Alpine.start();