verlok/vanilla-lazyload

Features

• Initial Page Load Optimizations - Reduces initial page load times by deferring the loading of images, videos, and iframes until they enter the viewport.
• Viewport-Based Asset Loaders - Implements a viewport-based asset loading system to defer resource downloads until elements become visible.
• Viewport Visibility Observers - Uses the IntersectionObserver API to track when elements enter the viewport to trigger resource loading.
• Resource Loading Triggers - Implements resource loading by swapping placeholder attributes with original source values to trigger network requests.
• IntersectionObserver Media Loaders - Provides a performance tool using the IntersectionObserver API to trigger media downloads and script execution on visibility.
• Lazy Loading Libraries - Provides a JavaScript library dedicated to deferring the loading of images, videos, iframes, and backgrounds.
• Image Lazy Loading - Defers the loading of CSS background images until the corresponding element enters the viewport.
• Native Lazy Loading Polyfills - Acts as a wrapper that uses browser native loading attributes where supported with a JavaScript fallback for older browsers.
• Native Loading Polyfills - Utilizes native browser loading attributes where supported and provides a JavaScript fallback for older environments.
• Iframe Lazy Loading - Postpones the loading of embedded iframes until they are visible to reduce initial page load time.
• Media Lazy Loading - Postpones the loading of images, videos, iframes, and animated SVGs until they enter the viewport.
• Video Lazy Loading - Delays the loading of video elements until they are visible to the user to preserve bandwidth.
• Viewport-Based Asset Loading - Manages the loading of media and scripts based on their visibility to the user using the IntersectionObserver API.
• Viewport-Aware Bandwidth Optimization - Saves data by canceling active downloads of media elements that exit the viewport before they finish loading.
• WebP Fallback Polyfills - Provides automatic WebP format delivery with fallbacks for browsers that do not support high-efficiency image types.
• Request Abort Controllers - Aborts active media downloads when elements exit the viewport to preserve bandwidth.
• Event-Driven Callbacks - Provides an event-driven system to execute custom JavaScript functions at specific loading lifecycle stages.
• Event Callbacks - Executes custom functions when elements enter the viewport, start loading, finish loading, or encounter errors.
• Deferred UI Initialization - Delays the loading and setup of complex UI components until they enter the viewport to improve startup speed.
• DOM Element Re-scanning - Updates visibility observers to handle and lazy load new elements added to a page asynchronously.
• Visibility-Triggered Actions - Triggers custom JavaScript functions when specific elements scroll into the user's view.
• Dynamic Asset Observation - Updates visibility observers to handle and lazy load new elements added to a page asynchronously.
• Dynamic Element Observation - Updates internal observers to detect and lazy load new elements added to the document asynchronously.
• Loading Error Recovery - Provides a callback system to assign fallback images when a lazy-loaded element fails to load.
• Loading State Markers - Uses CSS classes and callbacks to track and signal when lazy-loaded elements are loading, loaded, or failed.
• Responsive Image Loaders - Loads appropriate image resolutions and high-efficiency formats like WebP only when elements become visible.
• Network Connectivity Retries - Automatically attempts to reload media elements that failed due to temporary network connectivity loss.
• Resource Download Cancellation - Aborts the download of media elements that exit the viewport before they finish loading to optimize bandwidth.

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