refactor: enforce strict TypeScript linting rules

Upgrade ESLint config to use flat config with @typescript-eslint/strict-type-checked and stylistic-type-checked presets.

- Use defineConfig helper, scope to .ts files only
- Replace || with ??, convert type to interface, remove redundant type assertions and non-null assertions
- Annotate intentional violations (unbound-method, non-null-assertion) with eslint-disable
- Use querySelectorAll<T> for typed selection, Map over globalThis.Map
- Add @eslint/js dev dependency

eslint.config.js

@@ -1,24 +1,43 @@
-import tsParser from '@typescript-eslint/parser';
+import { defineConfig } from 'eslint/config';
 import tsPlugin from '@typescript-eslint/eslint-plugin';
 import prettierPlugin from 'eslint-plugin-prettier';
 import prettierConfig from 'eslint-config-prettier';
 
-export default [
+export default defineConfig([
   {
-    files: ['src/**/*.ts'],
+    ignores: ['dist/'],
+  },
+
+  ...tsPlugin.configs['flat/strict-type-checked'].map(c => ({
+    ...c,
+    files: ['**/*.ts'],
+  })),
+
+  ...tsPlugin.configs['flat/stylistic-type-checked'].map(c => ({
+    ...c,
+    files: ['**/*.ts'],
+  })),
+
+
+
+  {
+    files: ['**/*.ts'],
     languageOptions: {
-      parser: tsParser,
-      ecmaVersion: 2020,
-      sourceType: 'module',
+      parserOptions: { project: true },
     },
     plugins: {
-      '@typescript-eslint': tsPlugin,
       prettier: prettierPlugin,
     },
     rules: {
-      ...tsPlugin.configs.recommended.rules,
       ...prettierConfig.rules,
       'prettier/prettier': 'error',
     },
   },
-];
+
+  {
+    files: ['**/*.ts'],
+    rules: {
+      '@typescript-eslint/restrict-template-expressions': ['error', { allowNumber: true }],
+    },
+  },
+]);

package-lock.json

@@ -12,6 +12,7 @@
         "leaflet": "1.9.4"
       },
       "devDependencies": {
+        "@eslint/js": "^10.0.1",
         "@rollup/plugin-terser": "^1.0.0",
         "@rollup/plugin-typescript": "^12.3.0",
         "@types/leaflet": "1.9.21",
@@ -124,6 +125,27 @@
         "node": "^20.19.0 || ^22.13.0 || >=24"
       }
     },
+    "node_modules/@eslint/js": {
+      "version": "10.0.1",
+      "resolved": "https://registry.npmjs.org/@eslint/js/-/js-10.0.1.tgz",
+      "integrity": "sha512-zeR9k5pd4gxjZ0abRoIaxdc7I3nDktoXZk2qOv9gCNWx3mVwEn32VRhyLaRsDiJjTs0xq/T8mfPtyuXu7GWBcA==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": "^20.19.0 || ^22.13.0 || >=24"
+      },
+      "funding": {
+        "url": "https://eslint.org/donate"
+      },
+      "peerDependencies": {
+        "eslint": "^10.0.0"
+      },
+      "peerDependenciesMeta": {
+        "eslint": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/@eslint/object-schema": {
       "version": "3.0.5",
       "resolved": "https://registry.npmjs.org/@eslint/object-schema/-/object-schema-3.0.5.tgz",

package.json

@@ -39,6 +39,7 @@
     "leaflet": "1.9.4"
   },
   "devDependencies": {
+    "@eslint/js": "^10.0.1",
     "@rollup/plugin-terser": "^1.0.0",
     "@rollup/plugin-typescript": "^12.3.0",
     "@types/leaflet": "1.9.21",

src/components/leaflet-circle-marker.ts

@@ -24,11 +24,15 @@ export class LeafletCircleMarker extends WithProps(HTMLElement, PROPS) {
       [numAttr(this, PROPS, 'lat'), numAttr(this, PROPS, 'lng')],
       buildOptions(this, PROPS, ['lat', 'lng']),
     );
+    // The `on` method binds the function to `this`, we can ignore the error
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj.on('move', this.#onMove, this);
     registerChildren(this, this.#obj);
   }
 
   disconnectedCallback() {
+    // The `off` method binds the function to `this`, we can ignore the error
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj?.off('move', this.#onMove, this);
     unregisterChildren(this);
     this.#obj?.remove();

src/components/leaflet-circle.ts

@@ -24,11 +24,15 @@ export class LeafletCircle extends WithProps(HTMLElement, PROPS) {
       [numAttr(this, PROPS, 'lat'), numAttr(this, PROPS, 'lng')],
       buildOptions(this, PROPS, ['lat', 'lng']),
     );
+    // the on method binds the function to `this`, we can ignore the error
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj.on('move', this.#onMove, this);
     registerChildren(this, this.#obj);
   }
 
   disconnectedCallback() {
+    // the off method binds the function to `this`, we can ignore the error
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj?.off('move', this.#onMove, this);
     unregisterChildren(this);
     this.#obj?.remove();

src/components/leaflet-control-layers.ts

@@ -65,11 +65,14 @@ export class LeafletControlLayers extends WithProps(HTMLElement, PROPS) {
     const el = e.detail.element;
     const layer = e.detail.leafletObject;
     const name = el.getAttribute('name');
-    if (!name || !layer) return;
+    if (!name) return;
     const base = el.getAttribute('type') === 'base';
     const active = el.hasAttribute('active');
-    if (base) this.#obj!.addBaseLayer(layer, name);
-    else this.#obj!.addOverlay(layer, name);
+    if (base) {
+      this.#obj?.addBaseLayer(layer, name);
+    } else {
+      this.#obj?.addOverlay(layer, name);
+    }
     if (active) {
       this.dispatchEvent(
         new CustomEvent('leaflet-add-layer', { bubbles: true, detail: { layer } }),

src/components/leaflet-div-icon.ts

@@ -1,4 +1,4 @@
-import { DivIcon, DivIconOptions, Icon } from 'leaflet';
+import { DivIcon, DivIconOptions } from 'leaflet';
 import { defineProps, str } from '../core/props.ts';
 import { emitIconChanged } from '../core/register.ts';
 
@@ -12,10 +12,16 @@ const PROPS = defineProps({
   bgPos: str(),
 });
 
-const JSON_KEYS = new Set(['iconSize', 'iconAnchor', 'popupAnchor', 'tooltipAnchor', 'bgPos']);
+const JSON_KEYS = new Set<keyof typeof PROPS>([
+  'iconSize',
+  'iconAnchor',
+  'popupAnchor',
+  'tooltipAnchor',
+  'bgPos',
+]);
 
 export class LeafletDivIcon extends HTMLElement {
-  #obj?: Icon;
+  #obj?: DivIcon;
   #observer?: MutationObserver;
 
   connectedCallback() {
@@ -54,15 +60,17 @@ export class LeafletDivIcon extends HTMLElement {
   }
 
   #applyIcon() {
-    const opts: Record<string, unknown> = {};
+    const opts: Partial<DivIconOptions> = {};
     for (const [key, spec] of Object.entries(PROPS)) {
       const v = this.getAttribute(spec.attr);
       if (v === null) continue;
-      opts[key] = JSON_KEYS.has(key) ? JSON.parse(v) : v;
+      const typedKey = key as keyof typeof PROPS;
+      // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+      opts[typedKey as keyof DivIconOptions] = JSON_KEYS.has(typedKey) ? JSON.parse(v) : v;
     }
     const content = this.innerHTML;
     if (content) opts.html = content;
-    this.#obj = new DivIcon(opts as DivIconOptions) as unknown as Icon;
+    this.#obj = new DivIcon(opts);
   }
 }
 

src/components/leaflet-feature-group.ts

@@ -18,7 +18,7 @@ export class LeafletFeatureGroup extends HTMLElement {
     for (const [el, type] of getChildren(this) ?? []) {
       if (type === 'popup') this.#obj?.unbindPopup();
       else if (type === 'tooltip') this.#obj?.unbindTooltip();
-      else if (type === 'layer') this.#obj?.removeLayer(el as unknown as Layer);
+      else this.#obj?.removeLayer(el as unknown as Layer);
     }
     unregisterChildren(this);
     this.#obj?.remove();

src/components/leaflet-geojson.ts

@@ -2,6 +2,7 @@ import { GeoJSON, PathOptions, Layer } from 'leaflet';
 import { WithProps, defineProps, num, str, on } from '../core/props.ts';
 import { registerChildren, unregisterChildren, getChildren } from '../core/register.ts';
 import { buildOptions } from '../core/utils.ts';
+import type { GeoJsonObject } from 'geojson';
 
 const PROPS = defineProps({
   data: str(),
@@ -28,7 +29,7 @@ export class LeafletGeoJSON extends WithProps(HTMLElement, PROPS) {
 
   connectedCallback() {
     const raw = this.getAttribute('data');
-    const data = raw ? JSON.parse(raw) : undefined;
+    const data = raw ? (JSON.parse(raw) as GeoJsonObject) : null;
     const styleOpts = Object.fromEntries(
       Object.entries(buildOptions(this, PROPS, ['data'])).filter(([, v]) => v !== ''),
     );
@@ -40,7 +41,7 @@ export class LeafletGeoJSON extends WithProps(HTMLElement, PROPS) {
     for (const [el, type] of getChildren(this) ?? []) {
       if (type === 'popup') this.#obj?.unbindPopup();
       else if (type === 'tooltip') this.#obj?.unbindTooltip();
-      else if (type === 'layer') this.#obj?.removeLayer(el as unknown as Layer);
+      else this.#obj?.removeLayer(el as unknown as Layer);
     }
     unregisterChildren(this);
     this.#obj?.remove();
@@ -55,6 +56,7 @@ export class LeafletGeoJSON extends WithProps(HTMLElement, PROPS) {
     if (!this.#obj) return;
     if (name === 'data') {
       this.#obj.clearLayers();
+      // eslint-disable-next-line @typescript-eslint/no-unsafe-argument
       if (val) this.#obj.addData(JSON.parse(val));
     } else {
       const propName = PROP_BY_ATTR.get(name);

src/components/leaflet-image-overlay.ts

@@ -22,7 +22,7 @@ export class LeafletImageOverlay extends WithProps(HTMLElement, PROPS) {
   #obj?: ImageOverlay;
 
   connectedCallback() {
-    const url = this.getAttribute('url') || '';
+    const url = this.getAttribute('url') ?? '';
     this.#obj = new ImageOverlay(
       url,
       parseBoundsAttr(this),
@@ -49,9 +49,9 @@ export class LeafletImageOverlay extends WithProps(HTMLElement, PROPS) {
       this.#obj.setBounds(new LatLngBounds(parseBoundsAttr(this) as LatLngExpression[]));
     } else if (name === 'alt') {
       const el = this.#obj.getElement();
-      if (el) (el as HTMLImageElement).alt = val ?? '';
+      if (el) el.alt = val ?? '';
     } else {
-      setLayerAttr(this.#obj!, PROPS, PROP_BY_ATTR, name, val);
+      setLayerAttr(this.#obj, PROPS, PROP_BY_ATTR, name, val);
     }
   }
 }

src/components/leaflet-layer-group.ts

@@ -18,7 +18,7 @@ export class LeafletLayerGroup extends HTMLElement {
     for (const [el, type] of getChildren(this) ?? []) {
       if (type === 'popup') this.#obj?.unbindPopup();
       else if (type === 'tooltip') this.#obj?.unbindTooltip();
-      else if (type === 'layer') this.#obj?.removeLayer(el as unknown as Layer);
+      else this.#obj?.removeLayer(el as unknown as Layer);
     }
     unregisterChildren(this);
     this.#obj?.remove();

src/components/leaflet-map.ts

@@ -12,14 +12,14 @@ const PROPS = defineProps({
   lat: num(0, {
     viewState: true,
     event: 'moveend',
-    mapGet: (m: LMap) => m.getCenter()?.lat,
-    mapSet: (m: LMap, v: number) => m.setView([v, m.getCenter()?.lng ?? 0], m.getZoom()),
+    mapGet: (m: LMap) => m.getCenter().lat,
+    mapSet: (m: LMap, v: number) => m.setView([v, m.getCenter().lng], m.getZoom()),
   }),
   lng: num(0, {
     viewState: true,
     event: 'moveend',
-    mapGet: (m: LMap) => m.getCenter()?.lng,
-    mapSet: (m: LMap, v: number) => m.setView([m.getCenter()?.lat ?? 0, v], m.getZoom()),
+    mapGet: (m: LMap) => m.getCenter().lng,
+    mapSet: (m: LMap, v: number) => m.setView([m.getCenter().lat, v], m.getZoom()),
   }),
   zoom: num(2, {
     viewState: true,
@@ -81,7 +81,7 @@ const PROPS = defineProps({
 
 type PropName = keyof typeof PROPS;
 
-const ATTR_TO_PROP = new globalThis.Map<string, PropName>(
+const ATTR_TO_PROP = new Map<string, PropName>(
   (Object.entries(PROPS) as [PropName, PropDef][]).map(([name, spec]) => [spec.attr, name]),
 );
 
@@ -98,7 +98,7 @@ export class LeafletMap extends TypedBase {
   #container!: HTMLDivElement;
   #cssLink?: HTMLLinkElement;
   #syncing = false;
-  #mapEventHandlers = new globalThis.Map<string, () => void>();
+  #mapEventHandlers = new Map<string, () => void>();
   #resizeObserver?: ResizeObserver;
 
   static get observedAttributes(): string[] {
@@ -113,7 +113,7 @@ export class LeafletMap extends TypedBase {
         Object.defineProperty(LeafletMap.prototype, propName, {
           get(this: LeafletMap) {
             const val = spec.mapGet && this.#map ? spec.mapGet(this.#map) : undefined;
-            return val !== undefined ? val : +(this.getAttribute(spec.attr) ?? spec.default);
+            return val ?? +(this.getAttribute(spec.attr) ?? spec.default);
           },
           set(this: LeafletMap, v: number) {
             if (spec.event) {
@@ -157,9 +157,11 @@ export class LeafletMap extends TypedBase {
       this.#container = document.createElement('div');
       this.#container.style.width = '100%';
       this.#container.style.height = '100%';
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
       this.shadowRoot!.appendChild(this.#container);
       const style = document.createElement('style');
       style.textContent = ':host { display: block; width: 100%; height: 400px; }';
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
       this.shadowRoot!.appendChild(style);
     }
     this.#applyCss();
@@ -180,7 +182,7 @@ export class LeafletMap extends TypedBase {
     this.#resizeObserver.observe(this);
 
     // Register one handler per unique map event, updating all props that share it
-    const groups = new globalThis.Map<string, NumProp[]>();
+    const groups = new Map<string, NumProp[]>();
     for (const spec of Object.values(PROPS) as PropDef[]) {
       if (spec.kind === 'num' && spec.event && spec.mapGet) {
         const g = groups.get(spec.event) ?? [];
@@ -254,11 +256,11 @@ export class LeafletMap extends TypedBase {
     }
 
     const customUrl = this.hasAttribute('css-url');
-    const url = customUrl ? this.getAttribute('css-url')! : DEFAULT_CSS_URL;
+    const url = customUrl ? this.getAttribute('css-url') : DEFAULT_CSS_URL;
 
-    let integrity: string | undefined;
+    let integrity: string | null = null;
     if (this.hasAttribute('css-integrity')) {
-      integrity = this.getAttribute('css-integrity')!;
+      integrity = this.getAttribute('css-integrity') ?? '';
     } else if (!customUrl) {
       integrity = DEFAULT_CSS_INTEGRITY;
     }
@@ -273,14 +275,14 @@ export class LeafletMap extends TypedBase {
 
     const link = document.createElement('link');
     link.rel = 'stylesheet';
-    link.href = url;
+    link.href = url ?? '';
     if (integrity) link.setAttribute('integrity', integrity);
     if (crossorigin !== undefined) link.setAttribute('crossorigin', crossorigin);
     sr.appendChild(link);
     this.#cssLink = link;
 
     // Derive marker icon path from the CSS URL (replaces leaflet.css → images/)
-    Icon.Default.imagePath = url.replace(/\/[^/]+$/, '/images/');
+    Icon.Default.imagePath = url?.replace(/\/[^/]+$/, '/images/');
   }
 
   #syncAttr(name: string, value: string) {
@@ -303,12 +305,12 @@ export class LeafletMap extends TypedBase {
         if (this.hasAttribute(spec.attr)) o[propName] = true;
       }
     }
-    return o as MapOptions;
+    return o;
   }
 
   #handleLeafletRegister = (e: LeafletRegisterEvent) => {
     e.stopPropagation();
-    if (this.#map && e.detail.leafletObject) {
+    if (this.#map) {
       e.detail.leafletObject.addTo(this.#map);
     }
   };

src/components/leaflet-marker.ts

@@ -24,12 +24,14 @@ export class LeafletMarker extends WithProps(HTMLElement, PROPS) {
       [numAttr(this, PROPS, 'lat'), numAttr(this, PROPS, 'lng')],
       buildOptions(this, PROPS, ['lat', 'lng']),
     );
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj.on('dragend move', this.#onChange, this);
     registerChildren(this, this.#obj);
     this.addEventListener('icon-changed', this.#onIconChanged);
   }
 
   disconnectedCallback() {
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj?.off('dragend move', this.#onChange, this);
     this.removeEventListener('icon-changed', this.#onIconChanged);
     unregisterChildren(this);
@@ -55,7 +57,7 @@ export class LeafletMarker extends WithProps(HTMLElement, PROPS) {
       const el = this.#obj.getElement();
       if (el) (el as HTMLImageElement).alt = val ?? '';
     } else {
-      setLayerAttr(this.#obj!, PROPS, PROP_BY_ATTR, name, val);
+      setLayerAttr(this.#obj, PROPS, PROP_BY_ATTR, name, val);
     }
   }
 
@@ -68,11 +70,11 @@ export class LeafletMarker extends WithProps(HTMLElement, PROPS) {
     this.#syncing = false;
   }
 
-  #onIconChanged(e: LeafletIconChangedEvent) {
+  #onIconChanged = (e: LeafletIconChangedEvent) => {
     if (!this.#obj) return;
     if (e.detail.icon) this.#obj.setIcon(e.detail.icon);
     else this.#obj.setIcon(new Icon.Default());
-  }
+  };
 }
 
 customElements.define('leaflet-marker', LeafletMarker);

src/components/leaflet-polygon.ts

@@ -22,7 +22,9 @@ export class LeafletPolygon extends WithProps(HTMLElement, PROPS) {
     registerChildren(this, this.#obj);
 
     this.addEventListener('line-updated', this.#syncCoords);
-    this.#observer = new MutationObserver(() => this.#syncCoords());
+    this.#observer = new MutationObserver(() => {
+      this.#syncCoords();
+    });
     this.#observer.observe(this, { childList: true });
   }
 
@@ -51,7 +53,7 @@ export class LeafletPolygon extends WithProps(HTMLElement, PROPS) {
   };
 
   #getCoords(): [number, number][] {
-    const lines = Array.from(this.querySelectorAll('leaflet-line')) as LeafletLine[];
+    const lines: LeafletLine[] = Array.from(this.querySelectorAll('leaflet-line'));
     return lines.map((line) => line.latlng);
   }
 }

src/components/leaflet-polyline.ts

@@ -22,7 +22,9 @@ export class LeafletPolyline extends WithProps(HTMLElement, PROPS) {
     registerChildren(this, this.#obj);
 
     this.addEventListener('line-updated', this.#syncCoords);
-    this.#observer = new MutationObserver(() => this.#syncCoords());
+    this.#observer = new MutationObserver(() => {
+      this.#syncCoords();
+    });
     this.#observer.observe(this, { childList: true });
   }
 
@@ -51,7 +53,7 @@ export class LeafletPolyline extends WithProps(HTMLElement, PROPS) {
   };
 
   #getCoords(): [number, number][] {
-    const lines = Array.from(this.querySelectorAll('leaflet-line')) as LeafletLine[];
+    const lines = Array.from(this.querySelectorAll<LeafletLine>('leaflet-line'));
     return lines.map((line) => line.latlng);
   }
 }

src/components/leaflet-popup.ts

@@ -26,6 +26,7 @@ export class LeafletPopup extends WithProps(HTMLElement, PROPS) {
     if (this.hasAttribute('lat') && this.hasAttribute('lng')) {
       this.#obj.setLatLng([numAttr(this, PROPS, 'lat'), numAttr(this, PROPS, 'lng')]);
     }
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj.on('move', this.#onChange, this);
     registerWithParent(this, this.#obj);
 
@@ -40,6 +41,7 @@ export class LeafletPopup extends WithProps(HTMLElement, PROPS) {
   }
 
   disconnectedCallback() {
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj?.off('move', this.#onChange, this);
     this.#observer?.disconnect();
     this.#observer = undefined;

src/components/leaflet-svg-overlay.ts

@@ -22,6 +22,7 @@ export class LeafletSVGOverlay extends WithProps(HTMLElement, PROPS) {
     const svg = this.querySelector('svg');
     const dummy = !svg ? document.createElementNS('http://www.w3.org/2000/svg', 'svg') : undefined;
     this.#obj = new SVGOverlay(
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
       svg ?? dummy!,
       parseBoundsAttr(this),
       buildOptions(this, PROPS, ['bounds']) as ImageOverlayOptions,
@@ -44,7 +45,7 @@ export class LeafletSVGOverlay extends WithProps(HTMLElement, PROPS) {
     if (name === 'bounds') {
       this.#obj.setBounds(new LatLngBounds(parseBoundsAttr(this) as LatLngExpression[]));
     } else {
-      setLayerAttr(this.#obj!, PROPS, PROP_BY_ATTR, name, val);
+      setLayerAttr(this.#obj, PROPS, PROP_BY_ATTR, name, val);
     }
   }
 }

src/components/leaflet-tile-layer-wms.ts

@@ -19,7 +19,7 @@ export class LeafletTileLayerWMS extends WithProps(HTMLElement, PROPS) {
   #obj?: TileLayer.WMS;
 
   connectedCallback() {
-    const url = this.getAttribute('url') || '';
+    const url = this.getAttribute('url') ?? '';
     this.#obj = new TileLayer.WMS(url, buildOptions(this, PROPS, ['url']));
     registerChildren(this, this.#obj);
   }
@@ -41,8 +41,8 @@ export class LeafletTileLayerWMS extends WithProps(HTMLElement, PROPS) {
     } else {
       const propName = PROP_BY_ATTR.get(name);
       if (!propName) return;
-      const spec = PROPS[propName as keyof typeof PROPS];
-      if (!setLayerAttr(this.#obj!, PROPS, PROP_BY_ATTR, name, val)) {
+      const spec = PROPS[propName];
+      if (!setLayerAttr(this.#obj, PROPS, PROP_BY_ATTR, name, val)) {
         const value = spec.kind === 'bool-on' ? val !== null : parseAttributeValue(val);
         (this.#obj.setParams as unknown as (params: Record<string, unknown>) => void)({
           [propName]: value,

src/components/leaflet-tile-layer.ts

@@ -18,7 +18,7 @@ export class LeafletTileLayer extends WithProps(HTMLElement, PROPS) {
   #obj?: TileLayer;
 
   connectedCallback() {
-    const url = this.getAttribute('url') || '';
+    const url = this.getAttribute('url') ?? '';
     this.#obj = new TileLayer(url, buildOptions(this, PROPS, ['url']));
     registerChildren(this, this.#obj);
   }
@@ -38,7 +38,7 @@ export class LeafletTileLayer extends WithProps(HTMLElement, PROPS) {
     if (name === 'url') {
       if (val) this.#obj.setUrl(val);
     } else {
-      setLayerAttr(this.#obj!, PROPS, PROP_BY_ATTR, name, val);
+      setLayerAttr(this.#obj, PROPS, PROP_BY_ATTR, name, val);
     }
   }
 }

src/components/leaflet-tooltip.ts

@@ -27,6 +27,7 @@ export class LeafletTooltip extends WithProps(HTMLElement, PROPS) {
     if (this.hasAttribute('lat') && this.hasAttribute('lng')) {
       this.#obj.setLatLng([numAttr(this, PROPS, 'lat'), numAttr(this, PROPS, 'lng')]);
     }
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj.on('move', this.#onChange, this);
     registerWithParent(this, this.#obj);
 
@@ -41,6 +42,7 @@ export class LeafletTooltip extends WithProps(HTMLElement, PROPS) {
   }
 
   disconnectedCallback() {
+    // eslint-disable-next-line @typescript-eslint/unbound-method
     this.#obj?.off('move', this.#onChange, this);
     this.#observer?.disconnect();
     this.#observer = undefined;

src/components/leaflet-video-overlay.ts

@@ -23,7 +23,7 @@ export class LeafletVideoOverlay extends WithProps(HTMLElement, PROPS) {
   #obj?: VideoOverlay;
 
   connectedCallback() {
-    const url = this.getAttribute('url') || '';
+    const url = this.getAttribute('url') ?? '';
     this.#obj = new VideoOverlay(
       url,
       parseBoundsAttr(this),
@@ -59,10 +59,10 @@ export class LeafletVideoOverlay extends WithProps(HTMLElement, PROPS) {
         if (name === 'loop') el.loop = val !== null;
         else if (name === 'autoplay') el.autoplay = val !== null;
         else if (name === 'muted') el.muted = val !== null;
-        else if (name === 'playsinline') el.playsInline = val !== null;
+        else el.playsInline = val !== null;
       }
     } else {
-      setLayerAttr(this.#obj!, PROPS, PROP_BY_ATTR, name, val);
+      setLayerAttr(this.#obj, PROPS, PROP_BY_ATTR, name, val);
     }
   }
 

src/core/props.ts

@@ -1,31 +1,31 @@
-export type NumProp<T = unknown> = {
+export interface NumProp<T = unknown> {
   kind: 'num';
   attr: string;
   default: number;
-  mapGet?: (m: T) => number | undefined;
-  mapSet?: (m: T, v: number) => void;
+  mapGet?(m: T): number | undefined;
+  mapSet?(m: T, v: number): void;
   viewState?: boolean;
   event?: string;
-};
+}
 
-export type StrProp = {
+export interface StrProp {
   kind: 'str';
   attr: string;
   default: string;
-};
+}
 
-export type BoolOnProp = {
+export interface BoolOnProp {
   kind: 'bool-on';
   attr: string;
-};
+}
 
-export type BoolOffProp<T = unknown> = {
+export interface BoolOffProp<T = unknown> {
   kind: 'bool-off';
   attr: string;
-  mapSet?: (m: T, enabled: boolean) => void;
-};
+  mapSet?(m: T, enabled: boolean): void;
+}
 
-export type PropDef = NumProp<unknown> | StrProp | BoolOnProp | BoolOffProp<unknown>;
+export type PropDef = NumProp | StrProp | BoolOnProp | BoolOffProp;
 
 export type PropTypeOf<T extends PropDef> = T extends NumProp
   ? number
@@ -44,34 +44,46 @@ type StrPropInput = OptionalAttr<StrProp>;
 type BoolOnPropInput = OptionalAttr<BoolOnProp>;
 type BoolOffPropInput<T = unknown> = OptionalAttr<BoolOffProp<T>>;
 
-type PropDefInput =
-  | NumPropInput<unknown>
-  | StrPropInput
-  | BoolOnPropInput
-  | BoolOffPropInput<unknown>;
+type PropDefInput = NumPropInput | StrPropInput | BoolOnPropInput | BoolOffPropInput;
+
+type ValueFor<T, K extends keyof T> = T[K];
 
-type PropDefFromInput<T> =
-  T extends NumPropInput<infer U>
+type PropDefFromInput<T extends PropDefInput, Key extends string> = (T extends NumPropInput<infer U>
   ? NumProp<U>
   : T extends { kind: 'str' }
     ? StrProp
     : T extends BoolOffPropInput<infer U>
       ? BoolOffProp<U>
-        : BoolOnProp;
+      : BoolOnProp) & { attr: AttributeValue<T, Key> };
+
+type AttributeValue<T extends PropDefInput, Key extends string> = T extends { attr: string }
+  ? ValueFor<T, 'attr'>
+  : T extends BoolOffPropInput
+    ? AsDisableKebab<Key>
+    : AsKebab<Key>;
+
+type AsKebab<T extends string> = T extends `${infer L}${infer R}`
+  ? `${L extends Uppercase<L> ? '-' : ''}${Lowercase<L>}${AsKebab<R>}`
+  : T;
+
+type AsDisableKebab<T extends string> = `disable-${AsKebab<T>}`;
+
+function disableCamelToKebab<S extends string>(s: S): AsDisableKebab<S> {
+  return ('disable-' + s.replace(/[A-Z]/g, (c) => '-' + c.toLowerCase())) as AsDisableKebab<S>;
+}
 
 function camelToKebab(s: string): string {
   return s.replace(/[A-Z]/g, (c) => '-' + c.toLowerCase());
 }
 
 export function num<T = unknown>(
-  def: number = 0,
-  opts?: string | (Omit<NumProp<T>, 'kind' | 'default' | 'attr'> & { attr?: string }),
+  def = 0,
+  opts?: Omit<NumProp<T>, 'kind' | 'default' | 'attr'> & { attr?: string },
 ): NumPropInput<T> {
-  if (typeof opts === 'string') opts = { attr: opts };
-  return { kind: 'num', default: def, ...opts } as NumPropInput<T>;
+  return { kind: 'num', default: def, ...opts };
 }
 
-export function str(def: string = '', attr?: string): StrPropInput {
+export function str(def = '', attr?: string): StrPropInput {
   return { kind: 'str', default: def, ...(attr ? { attr } : {}) };
 }
 
@@ -80,21 +92,21 @@ export function on(attr?: string): BoolOnPropInput {
 }
 
 export function off<T = unknown>(mapSet?: (m: T, enabled: boolean) => void): BoolOffPropInput<T> {
-  return { kind: 'bool-off', ...(mapSet ? { mapSet } : {}) } as BoolOffPropInput<T>;
+  return { kind: 'bool-off', ...(mapSet ? { mapSet } : {}) };
 }
 
-export function defineProps<T extends Record<string, unknown>>(
+export function defineProps<T extends Record<string, PropDefInput>>(
   input: T,
-): { [K in keyof T]: PropDefFromInput<T[K]> } {
+): { [K in keyof T]: PropDefFromInput<T[K], Extract<K, string>> } {
   const output = {} as Record<string, PropDef>;
   for (const key of Object.keys(input)) {
-    const val = input[key] as PropDefInput;
+    const val = input[key];
     const { attr: override, ...rest } = val as unknown as Record<string, unknown>;
     const attr =
-      override ?? (rest.kind === 'bool-off' ? 'disable-' + camelToKebab(key) : camelToKebab(key));
-    output[key] = { ...rest, attr } as PropDef;
+      override ?? (rest.kind === 'bool-off' ? disableCamelToKebab(key) : camelToKebab(key));
+    output[key] = { ...(rest as object), attr } as PropDef;
   }
-  return output as unknown as { [K in keyof T]: PropDefFromInput<T[K]> };
+  return output as unknown as { [K in keyof T]: PropDefFromInput<T[K], Extract<K, string>> };
 }
 
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -126,6 +138,7 @@ function definePropAccessors(proto: object, props: Record<string, PropDef>) {
       set(v: unknown) {
         const el = this as HTMLElement;
         if (spec.kind === 'bool-on') el.toggleAttribute(spec.attr, !!v);
+        // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
         else el.setAttribute(spec.attr, `${v}`);
       },
       configurable: true,

src/core/register.ts

@@ -1,4 +1,4 @@
-import { Icon, Layer, LayerGroup, Popup, Tooltip } from 'leaflet';
+import { DivIcon, Icon, Layer, LayerGroup, Popup, Tooltip } from 'leaflet';
 import { registerWithParent } from './utils.ts';
 
 // Custom event type for the bubbling registration protocol. Carries the
@@ -22,7 +22,7 @@ declare global {
   }
 }
 
-export function emitIconChanged(el: HTMLElement, icon: Icon | null | undefined) {
+export function emitIconChanged(el: HTMLElement, icon: Icon | DivIcon | null | undefined) {
   el.dispatchEvent(
     new CustomEvent('icon-changed', {
       bubbles: true,

src/core/utils.ts

@@ -24,7 +24,7 @@ export function parseBoundsAttr(el: HTMLElement): LatLngBoundsExpression {
 // For example, { fillColor: { attr: 'fill-color' } } becomes
 // { 'fill-color' → 'fillColor' }. Used by setLayerAttr to find the
 // Leaflet setter name when an attribute changes at runtime.
-export function buildAttrMap(props: Record<string, PropDef>): Map<string, string> {
+export function buildAttrMap<T extends Record<string, PropDef>>(props: T): Map<string, keyof T> {
   return new Map(Object.entries(props).map(([name, spec]) => [spec.attr, name]));
 }
 
@@ -44,7 +44,7 @@ export function setLayerAttr(
 ): boolean {
   const propName = attrMap.get(name);
   if (!propName) return false;
-  const spec = props[propName as keyof typeof props];
+  const spec = props[propName];
   const setter = `set${propName.charAt(0).toUpperCase()}${propName.slice(1)}`;
   const fn = (obj as Record<string, unknown>)[setter];
   if (typeof fn === 'function') {