amorey/sentineljs

Health v2 · maintenance only

Adoption not part of the score

1131 stars · 38 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

SentinelJS is a tiny (668 bytes) JavaScript library that detects new DOM nodes matching CSS selectors using dynamically-defined @keyframes animation rules and animationstart events. It lets you register watch functions that fire whenever matching elements are added to the DOM, useful for implementing custom elements and in-place DOM modifications.

Use cases

• detect when a new DOM element matching a CSS selector is added
• implement custom elements without a framework
• watch for dynamically injected nodes in the DOM
• replace MutationObserver with a faster selector-based watch
• auto-initialize third-party widgets on newly inserted elements

When to choose

• you need a tiny, dependency-free way to react to new DOM nodes by CSS selector
• MutationObserver performance overhead is a concern for large documents
• you want lightweight custom-element-like behavior in older browsers

When to avoid

• you need to detect elements with display:none styling (SentinelJS cannot see them)
• your CSS already uses animation-name on overlapping selectors, causing conflicts
• you need to observe attribute changes or node removals, not just additions

Facets

library · maturity maintenance

ui-components middleware web-development frontend developer-tools browser dom-watching css-selectors custom-elements animationstart micro-library mutation-observer-alternative javascript

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