rrweb: A Deep Dive into Web Page Recording and Replay Mechanism

rrweb is an open-source library designed for recording and replaying web page interactions. Unlike traditional screen recording tools that capture video, rrweb records DOM state changes as JSON arrays, preserving exact element positions, attributes, and user actions. This approach allows for lightweight storage and lossless replay of complex web sessions.

The core architecture consists of three main components: rrweb for recording DOM mutations via MutationObserver , rrweb-snapshot for node serialization and DOM reconstruction, and rrweb-player for playback with custom UI controls. The recording process captures incremental changes through event-based serialization, while replay reconstructs the DOM using XState for state management.

Key advantages include user-transparent recording (no browser permissions required), JSON-based storage efficiency, and precise DOM recreation. The system handles complex scenarios like node movement and attribute changes through a combination of double-linked lists for deferred serialization and incremental snapshot processing. Playback maintains synchronization via requestAnimationFrame -based timing.

Compared to WebRTC-based solutions, rrweb offers better storage efficiency, no user interaction requirements, and full DOM fidelity. The library's implementation demonstrates advanced techniques in DOM manipulation tracking and state-driven replay systems.