A lightweight JavaScript library for monitoring element visibility during scrolling with a fast, dependency-free API.
ScrollMonitor is a lightweight JavaScript library that monitors DOM elements as they scroll into or out of the viewport. It provides watcher objects to track element visibility and trigger events, solving the need for performant scroll-based interactions without heavy dependencies. It supports both body scrolling and custom scroll containers.
Frontend developers building scroll-driven interfaces, animations, or dynamic content loading who need a fast, dependency-free solution for element visibility tracking.
Developers choose ScrollMonitor for its exceptional performance—minimizing DOM touches and memory overhead—and its flexible API that supports offsets, locking, and container-based scrolling without relying on external libraries.
A simple and fast API to monitor elements as you scroll
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Only touches the DOM twice per scroll event with minimal memory overhead, making it efficient for creating many watchers without slowing down the page.
Supports monitoring DOM elements, objects with top/bottom properties, numbers, jQuery objects, NodeLists, or CSS selectors, offering flexibility in what to track.
Allows creating scroll monitors for any scrollable element beyond the body, enabling complex nested scrolling scenarios as shown in the demos.
Provides events like enterViewport, exitViewport, and offset options to trigger actions precisely when elements are near the viewport edge.
Enables watchers to lock positions, which is ideal for implementing fixed elements or scroll-based animations without recalculations.
The README explicitly states the script cannot be put in the head, requiring careful loading in the body which may impact initial page performance or SEO strategies.
Demos acknowledge that scrolling within custom containers (divs) is much slower than body scrolling, a performance trade-off for complex UIs.
For framework integration like React, additional libraries (scrollmonitor-hooks, scrollmonitor-react) are required, adding complexity compared to native solutions.
Focuses solely on monitoring without providing scroll animations or UI components, necessitating extra code for visual effects beyond visibility tracking.