Performance optimization for Amazon: background throttling, lazy loading, and layout stabilization.
// ==UserScript==
// @name Amazon Page Smoother
// @namespace http://tampermonkey.net/
// @version 0.1.1
// @description Performance optimization for Amazon: background throttling, lazy loading, and layout stabilization.
// @license Unlicense
// @author VeleSila
// @match https://www.amazon.com/*
// @match https://www.amazon.co.jp/*
// @match https://www.amazon.co.uk/*
// @match https://www.amazon.es/*
// @match https://www.amazon.fr/*
// @match https://www.amazon.de/*
// @match https://www.amazon.it/*
// @match https://www.amazon.ca/*
// @match https://www.amazon.com.au/*
// @exclude */cart/*
// @exclude */buy/*
// @exclude */checkout/*
// @exclude */gp/buy/*
// @grant GM_addStyle
// @run-at document-start
// ==/UserScript==
(function() {
'use strict';
/**
* CONFIGURATION
*/
const CONFIG = {
// Number of images to load with high priority (Above the fold approximation)
HIGH_PRIORITY_COUNT: 4,
// Debounce delay for the mutation observer (ms)
DEBOUNCE_DELAY_MS: 300
};
/**
* 1. CRITICAL SAFETY CHECK
* Immediately exit on sensitive pages to prevent interference with payments.
*/
const sensitivePaths = /(checkout|signin|payment|addressselect|huc)/i;
if (sensitivePaths.test(window.location.pathname)) {
return;
}
/**
* 2. CSS OPTIMIZER
* Uses modern CSS containment to prevent rendering off-screen content.
*/
function injectOptimizedStyles() {
const css = `
/* Optimize Search Results */
.s-main-slot .s-result-item {
content-visibility: auto;
contain-intrinsic-size: 1px 350px;
}
/* GPU Acceleration for Product Images */
img.s-image {
transform: translateZ(0);
will-change: opacity;
}
/* Defer Footer Rendering */
#navFooter {
content-visibility: auto;
contain-intrinsic-size: 1px 600px;
}
`;
if (typeof GM_addStyle === 'function') {
GM_addStyle(css);
} else {
const style = document.createElement('style');
style.textContent = css;
document.head.appendChild(style);
}
}
/**
* 3. RESOURCE OPTIMIZER
* Applies lazy loading and fetch priority attributes.
*/
function optimizeResources(rootNode = document) {
// Select images that haven't been optimized yet
const images = rootNode.querySelectorAll('img:not([data-opt])');
if (images.length === 0) return;
// Check for browser support
const supportsPriority = 'fetchPriority' in HTMLImageElement.prototype;
for (let i = 0, len = images.length; i < len; i++) {
const img = images[i];
// Mark as processed
img.dataset.opt = '1';
// 1. Footer Images: Always low priority and lazy
if (img.closest('#navFooter')) {
img.loading = 'lazy';
img.decoding = 'async';
if (supportsPriority) img.fetchPriority = 'low';
continue;
}
// 2. Product Images (Search results)
if (img.classList.contains('s-image')) {
// Heuristic: The first few images found in the DOM are likely "Above the fold"
if (i < CONFIG.HIGH_PRIORITY_COUNT) {
img.loading = 'eager';
if (supportsPriority) img.fetchPriority = 'high';
} else {
img.loading = 'lazy';
img.decoding = 'async';
if (supportsPriority) img.fetchPriority = 'low';
}
continue;
}
// 3. General Fallback for other images
if (!img.hasAttribute('loading')) {
img.loading = 'lazy';
img.decoding = 'async';
}
}
}
/**
* 4. INITIALIZATION & OBSERVER
*/
function main() {
try {
injectOptimizedStyles();
// Initial pass
optimizeResources(document);
// Debounced Observer for dynamic content
let debounceTimer;
const observer = new MutationObserver((mutations) => {
let hasNewNodes = false;
for (const m of mutations) {
if (m.addedNodes.length > 0) {
hasNewNodes = true;
break;
}
}
if (!hasNewNodes) return;
clearTimeout(debounceTimer);
debounceTimer = setTimeout(() => {
if ('requestIdleCallback' in window) {
requestIdleCallback(() => optimizeResources(document.body));
} else {
optimizeResources(document.body);
}
}, CONFIG.DEBOUNCE_DELAY_MS);
});
// Target the search slot specifically if it exists, otherwise fallback to body
const targetNode = document.querySelector('.s-main-slot') || document.body;
observer.observe(targetNode, {
childList: true,
subtree: true
});
} catch (error) {
// Silently fail
}
}
// Boot Logic
if (document.readyState === 'loading') {
document.addEventListener('DOMContentLoaded', main, { once: true });
} else {
main();
}
})();