bpmn-js is a mature, extensible JavaScript library for rendering and editing BPMN 2.0 diagrams in the browser. It provides a full-featured modeler (Viewer, NavigatedViewer, Modeler) built on top of diagram-js, with support for import/export of BPMN XML and SVG, undo/redo, copy/paste, element replacement, grid snapping, auto-layout, and a rich set of modeling behaviors that enforce BPMN semantic rules. The architecture follows a modular dependency injection pattern (didi) with event-driven communication, command interceptors for undoable operations, and pluggable providers for context pads, palettes, popup menus, and renderers. The codebase is well-tested with hundreds of integration and unit tests, and includes benchmarks for large diagrams. It is actively maintained by the bpmn.io team and used widely in workflow and process automation tools.

diagram-js is a modular, extensible JavaScript library for building interactive web-based diagram editors. It provides the foundational infrastructure—an event-driven architecture via EventBus, a command pattern with full undo/redo support via CommandStack, and a DI container (didi) for composing features as independent modules. The codebase includes core services (Canvas, ElementRegistry, GraphicsFactory) for managing SVG rendering, hit testing, and element lifecycle, along with a rich set of interaction features: drag-and-drop creation/move/resize/connect, snapping, grid snapping, auto-resize, auto-place, bendpoint editing, lasso selection, space tool, popup menus, context pads, palettes, search, overlays, copy/paste, and keyboard bindings. It is designed for downstream domain-specific editors (e.g., bpmn-js, dmn-js) which extend it via provider interfaces and rule systems. The library is well-tested with an extensive suite using Mocha/Chai/Sinon and runs on modern browsers. Its architecture emphasizes decoupling, extensibility, and reusable patterns.