leaflet-components/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Commands

npm run build      # tsc emits individual ESM modules to dist/ (no bundling)
npm run typecheck  # tsc --noEmit, then tsc -p tsconfig.test.json for test/
npm run lint       # oxlint over src/ and test/
npm run format     # Prettier formatting
npm run test       # vitest run
npm run test:watch # vitest, watch mode

Linting runs on oxlint, not ESLint/@typescript-eslint. This project pins typescript@^7.0.2, and @typescript-eslint has no released version that supports it (peer range caps at <6.1.0, and even loading @typescript-eslint/parser crashes against TS 7's package shape). oxlint has its own parser and doesn't touch the typescript package, so it works regardless of TS version — the tradeoff is no type-aware rules (no no-floating-promises, no-unnecessary-condition, etc.). Revisit once @typescript-eslint supports TS 7.

Testing

Tests run under Vitest + jsdom (test/**/*.test.ts), with a single setup file (test/setup.ts) that stubs ResizeObserver -- jsdom doesn't implement it, and leaflet-map.ts constructs one unconditionally. Real Leaflet objects work fine under jsdom for everything this library actually needs to verify (option/attribute wiring, event forwarding); no browser is required. Two things worth knowing:

• Some Leaflet DOM state (the <img>/<video> element behind an overlay, a marker's dragging handler) is only created in onAdd(), i.e. once the layer is actually added to a real map -- tests touching that state append through a <leaflet-map> rather than standalone.
• test/core/with-props.test.ts covers the WithProps mixin itself against a fake Leaflet-like class (no real Leaflet needed for most of it) -- the one exception is child registration (popup/tooltip/layer binding), which needs real Popup/Tooltip/Layer instances because #onChildRegister discriminates by instanceof, not duck typing.

test/** is excluded from the main tsconfig.json (so test code never ends up in dist/) and typechecked separately via tsconfig.test.json.

To preview components in a real browser, open index.html with any static-file server.

Architecture

This library wraps Leaflet.js as native Web Components (Custom Elements). Each HTML element maps 1:1 to a Leaflet object.

WithProps mixin: src/core/with-props.ts

The WithProps(Base, PROPS) mixin factory replaces the old LeafletElement base class. Each component defines a PROPS table (a const record mapping kebab-case attribute names to PropDef descriptors), then extends WithProps(HTMLElement, PROPS). The mixin handles:

• observedAttributes getter derived from the PROPS table keys.
• definePropAccessors — property getters/setters on the prototype that sync attributes.
• On connect, initOptions() builds a Leaflet options object from current attributes + PROPS defaults, then calls createLeafletObject().
• On attribute change, updateLeafletObject() by default dispatches to the matching Leaflet setter (e.g. setOpacity, setRadius). Components override this for custom attribute handling (e.g. lat/lng pairs).
• Every Leaflet event the created object fires is re-emitted on the element as leaflet:<type> (e.g. leaflet:zoomend, leaflet:dragend), carrying the original Leaflet event object as event.detail. This is generic and automatic: WithProps wraps the object's own fire() method, so no per-component or per-event-type registration is needed. Not bubbling — Leaflet already propagates layer events up to the map, so <leaflet-map> would otherwise see each one twice.

leaflet-map: src/components/leaflet-map.ts

LeafletMap extends HTMLElement directly and uses Shadow DOM. It is the root of the component tree and terminates all bubbling leaflet-register events by calling layer.addTo(this.map). Uses a ResizeObserver on the host element to call map.invalidateSize() automatically.

Child component pattern

All non-map components extend WithProps(HTMLElement, PROPS). To add a new component:

1. Define a PROPS = {...} const table mapping kebab-case attributes to PropDef entries.
2. Declare class LeafletFoo extends WithProps(HTMLElement, PROPS) implementing createLeafletObject(): L.Layer.
3. Override updateLeafletObject(name, val) only if the default setter-based update won't work (common for coordinate pairs).
4. Call customElements.define('leaflet-foo', LeafletFoo) at the bottom.
5. Export from src/index.ts.

Special cases

• leaflet-polygon uses <leaflet-line> children for vertices. The polygon collects lat/lng from child leaflet-line elements rather than having them as direct attributes.
• leaflet-popup / leaflet-tooltip: content comes from innerHTML, not attributes. leaflet-popup watches for DOM mutations to keep Leaflet in sync.
• leaflet-layer-group / leaflet-feature-group: passthrough containers built with WithProps({}) (an empty props table) — they have no options of their own, but still get the standard lifecycle, child registration, and leaflet: event forwarding for free. Children register themselves into them via the standard bubble mechanism.

Output

tsc compiles src/ → dist/ as individual ESM modules (.js + .d.ts + .d.ts.map) — no bundling step. Consumers import dist/index.js (or any individual module) directly; there is no CJS or UMD build. Leaflet is always external (never bundled). Imports within source use .ts extensions; rewriteRelativeImportExtensions in tsconfig strips them to .js in the tsc output (tsconfig.json:16).