[mod] client/simple: client plugins (#5406)

* [mod] client/simple: client plugins

Defines a new interface for client side *"plugins"* that coexist with server
side plugin system. Each plugin (e.g., `InfiniteScroll`) extends the base
`ts Plugin`. Client side plugins are independent and lazy‑loaded via `router.ts`
when their `load()` conditions are met. On each navigation request, all
applicable plugins are instanced.

Since these are client side plugins, we can only invoke them once DOM is fully
loaded. E.g. `Calculator` will not render a new `answer` block until fully
loaded and executed.

For some plugins, we might want to handle its availability in `settings.yml`
and toggle in UI, like we do for server side plugins. In that case, we extend
`py Plugin` instancing only the information and then checking client side if
[`settings.plugins`](https://github.com/inetol/searxng/blob/1ad832b1dc33f3f388da361ff2459b05dc86a164/client/simple/src/js/toolkit.ts#L134)
array has the plugin id.

* [mod] client/simple: rebuild static

23 files changed, 590 insertions, 364 deletions

diff --git a/client/simple/src/js/Plugin.ts b/client/simple/src/js/Plugin.ts
new file mode 100644
index 000000000..bd41ff909
--- /dev/null
+++ b/client/simple/src/js/Plugin.ts
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+/**
+ * Base class for client-side plugins.
+ *
+ * @remarks
+ * Handle conditional loading of the plugin in:
+ *
+ *   - client/simple/src/js/router.ts
+ *
+ * @abstract
+ */
+export abstract class Plugin {
+  /**
+   * Plugin name.
+   */
+  protected readonly id: string;
+
+  /**
+   * @remarks
+   * Don't hold references of this instance outside the class.
+   */
+  protected constructor(id: string) {
+    this.id = id;
+
+    void this.invoke();
+  }
+
+  private async invoke(): Promise<void> {
+    try {
+      console.debug(`[PLUGIN] ${this.id}: Running...`);
+      const result = await this.run();
+      if (!result) return;
+
+      console.debug(`[PLUGIN] ${this.id}: Running post-exec...`);
+      // @ts-expect-error
+      void (await this.post(result as NonNullable<Awaited<ReturnType<this["run"]>>>));
+    } catch (error) {
+      console.error(`[PLUGIN] ${this.id}:`, error);
+    } finally {
+      console.debug(`[PLUGIN] ${this.id}: Done.`);
+    }
+  }
+
+  /**
+   * Plugin goes here.
+   *
+   * @remarks
+   * The plugin is already loaded at this point. If you wish to execute
+   * conditions to exit early, consider moving the logic to:
+   *
+   *   - client/simple/src/js/router.ts
+   *
+   * ...to avoid unnecessarily loading this plugin on the client.
+   */
+  protected abstract run(): Promise<unknown>;
+
+  /**
+   * Post-execution hook.
+   *
+   * @remarks
+   * The hook is only executed if `#run()` returns a truthy value.
+   */
+  // @ts-expect-error
+  protected abstract post(result: NonNullable<Awaited<ReturnType<this["run"]>>>): Promise<void>;
+}
diff --git a/client/simple/src/js/core/index.ts b/client/simple/src/js/core/index.ts
deleted file mode 100644
index 59e64182c..000000000
--- a/client/simple/src/js/core/index.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-// SPDX-License-Identifier: AGPL-3.0-or-later
-
-import "./nojs.ts";
-import "./router.ts";
-import "./toolkit.ts";
-import "./listener.ts";
diff --git a/client/simple/src/js/core/listener.ts b/client/simple/src/js/core/listener.ts
deleted file mode 100644
index b8c0cbfd5..000000000
--- a/client/simple/src/js/core/listener.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-// SPDX-License-Identifier: AGPL-3.0-or-later
-
-import { listen } from "./toolkit.ts";
-
-listen("click", ".close", function (this: HTMLElement) {
-  (this.parentNode as HTMLElement)?.classList.add("invisible");
-});
diff --git a/client/simple/src/js/core/nojs.ts b/client/simple/src/js/core/nojs.ts
deleted file mode 100644
index 65c62dd90..000000000
--- a/client/simple/src/js/core/nojs.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-// SPDX-License-Identifier: AGPL-3.0-or-later
-
-import { ready } from "./toolkit.ts";
-
-ready(() => {
-  document.documentElement.classList.remove("no-js");
-  document.documentElement.classList.add("js");
-});
diff --git a/client/simple/src/js/core/router.ts b/client/simple/src/js/core/router.ts
deleted file mode 100644
index bea838713..000000000
--- a/client/simple/src/js/core/router.ts
+++ /dev/null
@@ -1,40 +0,0 @@
-// SPDX-License-Identifier: AGPL-3.0-or-later
-
-import { Endpoints, endpoint, ready, settings } from "./toolkit.ts";
-
-ready(
-  () => {
-    void import("../main/keyboard.ts");
-    void import("../main/search.ts");
-
-    if (settings.autocomplete) {
-      void import("../main/autocomplete.ts");
-    }
-  },
-  { on: [endpoint === Endpoints.index] }
-);
-
-ready(
-  () => {
-    void import("../main/keyboard.ts");
-    void import("../main/mapresult.ts");
-    void import("../main/results.ts");
-    void import("../main/search.ts");
-
-    if (settings.infinite_scroll) {
-      void import("../main/infinite_scroll.ts");
-    }
-
-    if (settings.autocomplete) {
-      void import("../main/autocomplete.ts");
-    }
-  },
-  { on: [endpoint === Endpoints.results] }
-);
-
-ready(
-  () => {
-    void import("../main/preferences.ts");
-  },
-  { on: [endpoint === Endpoints.preferences] }
-);
diff --git a/client/simple/src/js/index.ts b/client/simple/src/js/index.ts
new file mode 100644
index 000000000..7a9802f4f
--- /dev/null
+++ b/client/simple/src/js/index.ts
@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+// core
+void import.meta.glob(["./*.ts", "./util/**/.ts"], { eager: true });
diff --git a/client/simple/src/js/loader.ts b/client/simple/src/js/loader.ts
new file mode 100644
index 000000000..ed374a2d8
--- /dev/null
+++ b/client/simple/src/js/loader.ts
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import type { Plugin } from "./Plugin.ts";
+import { type EndpointsKeys, endpoint } from "./toolkit.ts";
+
+type Options =
+  | {
+      on: "global";
+    }
+  | {
+      on: "endpoint";
+      where: EndpointsKeys[];
+    };
+
+export const load = <T extends Plugin>(instance: () => Promise<T>, options: Options): void => {
+  if (!check(options)) return;
+
+  void instance();
+};
+
+const check = (options: Options): boolean => {
+  // biome-ignore lint/style/useDefaultSwitchClause: options is typed
+  switch (options.on) {
+    case "global": {
+      return true;
+    }
+    case "endpoint": {
+      if (!options.where.includes(endpoint)) {
+        // not on the expected endpoint
+        return false;
+      }
+
+      return true;
+    }
+  }
+};
diff --git a/client/simple/src/js/main/autocomplete.ts b/client/simple/src/js/main/autocomplete.ts
index 57788dfd5..7da197ddf 100644
--- a/client/simple/src/js/main/autocomplete.ts
+++ b/client/simple/src/js/main/autocomplete.ts
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
-import { assertElement, http, listen, settings } from "../core/toolkit.ts";
+import { http, listen, settings } from "../toolkit.ts";
+import { assertElement } from "../util/assertElement.ts";
 
 const fetchResults = async (qInput: HTMLInputElement, query: string): Promise<void> => {
   try {
diff --git a/client/simple/src/js/main/infinite_scroll.ts b/client/simple/src/js/main/infinite_scroll.ts
deleted file mode 100644
index b286bce37..000000000
--- a/client/simple/src/js/main/infinite_scroll.ts
+++ /dev/null
@@ -1,100 +0,0 @@
-// SPDX-License-Identifier: AGPL-3.0-or-later
-
-import { assertElement, http, settings } from "../core/toolkit.ts";
-
-const newLoadSpinner = (): HTMLDivElement => {
-  return Object.assign(document.createElement("div"), {
-    className: "loader"
-  });
-};
-
-const loadNextPage = async (onlyImages: boolean, callback: () => void): Promise<void> => {
-  const searchForm = document.querySelector<HTMLFormElement>("#search");
-  assertElement(searchForm);
-
-  const form = document.querySelector<HTMLFormElement>("#pagination form.next_page");
-  assertElement(form);
-
-  const action = searchForm.getAttribute("action");
-  if (!action) {
-    throw new Error("Form action not defined");
-  }
-
-  const paginationElement = document.querySelector<HTMLElement>("#pagination");
-  assertElement(paginationElement);
-
-  paginationElement.replaceChildren(newLoadSpinner());
-
-  try {
-    const res = await http("POST", action, { body: new FormData(form) });
-    const nextPage = await res.text();
-    if (!nextPage) return;
-
-    const nextPageDoc = new DOMParser().parseFromString(nextPage, "text/html");
-    const articleList = nextPageDoc.querySelectorAll<HTMLElement>("#urls article");
-    const nextPaginationElement = nextPageDoc.querySelector<HTMLElement>("#pagination");
-
-    document.querySelector("#pagination")?.remove();
-
-    const urlsElement = document.querySelector<HTMLElement>("#urls");
-    if (!urlsElement) {
-      throw new Error("URLs element not found");
-    }
-
-    if (articleList.length > 0 && !onlyImages) {
-      // do not add <hr> element when there are only images
-      urlsElement.appendChild(document.createElement("hr"));
-    }
-
-    urlsElement.append(...Array.from(articleList));
-
-    if (nextPaginationElement) {
-      const results = document.querySelector<HTMLElement>("#results");
-      results?.appendChild(nextPaginationElement);
-      callback();
-    }
-  } catch (error) {
-    console.error("Error loading next page:", error);
-
-    const errorElement = Object.assign(document.createElement("div"), {
-      textContent: settings.translations?.error_loading_next_page ?? "Error loading next page",
-      className: "dialog-error"
-    });
-    errorElement.setAttribute("role", "alert");
-    document.querySelector("#pagination")?.replaceChildren(errorElement);
-  }
-};
-
-const resultsElement: HTMLElement | null = document.getElementById("results");
-if (!resultsElement) {
-  throw new Error("Results element not found");
-}
-
-const onlyImages: boolean = resultsElement.classList.contains("only_template_images");
-const observedSelector = "article.result:last-child";
-
-const intersectionObserveOptions: IntersectionObserverInit = {
-  rootMargin: "320px"
-};
-
-const observer: IntersectionObserver = new IntersectionObserver((entries: IntersectionObserverEntry[]) => {
-  const [paginationEntry] = entries;
-
-  if (paginationEntry?.isIntersecting) {
-    observer.unobserve(paginationEntry.target);
-
-    void loadNextPage(onlyImages, () => {
-      const nextObservedElement = document.querySelector<HTMLElement>(observedSelector);
-      if (nextObservedElement) {
-        observer.observe(nextObservedElement);
-      }
-    }).then(() => {
-      // wait until promise is resolved
-    });
-  }
-}, intersectionObserveOptions);
-
-const initialObservedElement: HTMLElement | null = document.querySelector<HTMLElement>(observedSelector);
-if (initialObservedElement) {
-  observer.observe(initialObservedElement);
-}
diff --git a/client/simple/src/js/main/keyboard.ts b/client/simple/src/js/main/keyboard.ts
index f165a601a..7a8fa8e28 100644
--- a/client/simple/src/js/main/keyboard.ts
+++ b/client/simple/src/js/main/keyboard.ts
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
-import { assertElement, listen, mutable, settings } from "../core/toolkit.ts";
+import { listen, mutable, settings } from "../toolkit.ts";
+import { assertElement } from "../util/assertElement.ts";
 
 export type KeyBindingLayout = "default" | "vim";
 
diff --git a/client/simple/src/js/main/mapresult.ts b/client/simple/src/js/main/mapresult.ts
deleted file mode 100644
index 32bbec4fc..000000000
--- a/client/simple/src/js/main/mapresult.ts
+++ /dev/null
@@ -1,86 +0,0 @@
-// SPDX-License-Identifier: AGPL-3.0-or-later
-
-import { listen } from "../core/toolkit.ts";
-
-listen("click", ".searxng_init_map", async function (this: HTMLElement, event: Event) {
-  event.preventDefault();
-  this.classList.remove("searxng_init_map");
-
-  const {
-    View,
-    OlMap,
-    TileLayer,
-    VectorLayer,
-    OSM,
-    VectorSource,
-    Style,
-    Stroke,
-    Fill,
-    Circle,
-    fromLonLat,
-    GeoJSON,
-    Feature,
-    Point
-  } = await import("../pkg/ol.ts");
-  void import("ol/ol.css");
-
-  const { leafletTarget: target, mapLon, mapLat, mapGeojson } = this.dataset;
-
-  const lon = Number.parseFloat(mapLon || "0");
-  const lat = Number.parseFloat(mapLat || "0");
-  const view = new View({ maxZoom: 16, enableRotation: false });
-  const map = new OlMap({
-    target: target,
-    layers: [new TileLayer({ source: new OSM({ maxZoom: 16 }) })],
-    view: view
-  });
-
-  try {
-    const markerSource = new VectorSource({
-      features: [
-        new Feature({
-          geometry: new Point(fromLonLat([lon, lat]))
-        })
-      ]
-    });
-
-    const markerLayer = new VectorLayer({
-      source: markerSource,
-      style: new Style({
-        image: new Circle({
-          radius: 6,
-          fill: new Fill({ color: "#3050ff" })
-        })
-      })
-    });
-
-    map.addLayer(markerLayer);
-  } catch (error) {
-    console.error("Failed to create marker layer:", error);
-  }
-
-  if (mapGeojson) {
-    try {
-      const geoSource = new VectorSource({
-        features: new GeoJSON().readFeatures(JSON.parse(mapGeojson), {
-          dataProjection: "EPSG:4326",
-          featureProjection: "EPSG:3857"
-        })
-      });
-
-      const geoLayer = new VectorLayer({
-        source: geoSource,
-        style: new Style({
-          stroke: new Stroke({ color: "#3050ff", width: 2 }),
-          fill: new Fill({ color: "#3050ff33" })
-        })
-      });
-
-      map.addLayer(geoLayer);
-
-      view.fit(geoSource.getExtent(), { padding: [20, 20, 20, 20] });
-    } catch (error) {
-      console.error("Failed to create GeoJSON layer:", error);
-    }
-  }
-});
diff --git a/client/simple/src/js/main/preferences.ts b/client/simple/src/js/main/preferences.ts
index 620370ee5..eb8974bf2 100644
--- a/client/simple/src/js/main/preferences.ts
+++ b/client/simple/src/js/main/preferences.ts
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
-import { assertElement, http, listen, settings } from "../core/toolkit.ts";
+import { http, listen, settings } from "../toolkit.ts";
+import { assertElement } from "../util/assertElement.ts";
 
 let engineDescriptions: Record<string, [string, string]> | undefined;
 
diff --git a/client/simple/src/js/main/results.ts b/client/simple/src/js/main/results.ts
index 42298f9f8..b59032a2c 100644
--- a/client/simple/src/js/main/results.ts
+++ b/client/simple/src/js/main/results.ts
@@ -1,7 +1,8 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
 import "../../../node_modules/swiped-events/src/swiped-events.js";
-import { assertElement, listen, mutable, settings } from "../core/toolkit.ts";
+import { listen, mutable, settings } from "../toolkit.ts";
+import { assertElement } from "../util/assertElement.ts";
 
 let imgTimeoutID: number;
 
diff --git a/client/simple/src/js/main/search.ts b/client/simple/src/js/main/search.ts
index c7ce9e090..eecc1afb0 100644
--- a/client/simple/src/js/main/search.ts
+++ b/client/simple/src/js/main/search.ts
@@ -1,88 +1,49 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
-import { assertElement, listen, settings } from "../core/toolkit.ts";
+import { listen } from "../toolkit.ts";
+import { getElement } from "../util/getElement.ts";
 
-const submitIfQuery = (qInput: HTMLInputElement): void => {
-  if (qInput.value.length > 0) {
-    const search = document.getElementById("search") as HTMLFormElement | null;
-    search?.submit();
-  }
-};
-
-const updateClearButton = (qInput: HTMLInputElement, cs: HTMLElement): void => {
-  cs.classList.toggle("empty", qInput.value.length === 0);
-};
-
-const createClearButton = (qInput: HTMLInputElement): void => {
-  const cs = document.getElementById("clear_search");
-  assertElement(cs);
-
-  updateClearButton(qInput, cs);
-
-  listen("click", cs, (event: MouseEvent) => {
-    event.preventDefault();
-    qInput.value = "";
-    qInput.focus();
-    updateClearButton(qInput, cs);
-  });
-
-  listen("input", qInput, () => updateClearButton(qInput, cs), { passive: true });
-};
-
-const qInput = document.getElementById("q") as HTMLInputElement | null;
-assertElement(qInput);
+const searchForm: HTMLFormElement = getElement<HTMLFormElement>("search");
+const searchInput: HTMLInputElement = getElement<HTMLInputElement>("q");
+const searchReset: HTMLButtonElement = getElement<HTMLButtonElement>("clear_search");
 
 const isMobile: boolean = window.matchMedia("(max-width: 50em)").matches;
 const isResultsPage: boolean = document.querySelector("main")?.id === "main_results";
 
+const categoryButtons: HTMLButtonElement[] = Array.from(
+  document.querySelectorAll<HTMLButtonElement>("#categories_container button.category")
+);
+
+if (searchInput.value.length === 0) {
+  searchReset.classList.add("empty");
+}
+
 // focus search input on large screens
 if (!(isMobile || isResultsPage)) {
-  qInput.focus();
+  searchInput.focus();
 }
 
 // On mobile, move cursor to the end of the input on focus
 if (isMobile) {
-  listen("focus", qInput, () => {
+  listen("focus", searchInput, () => {
     // Defer cursor move until the next frame to prevent a visual jump
     requestAnimationFrame(() => {
-      const end = qInput.value.length;
-      qInput.setSelectionRange(end, end);
-      qInput.scrollLeft = qInput.scrollWidth;
+      const end = searchInput.value.length;
+      searchInput.setSelectionRange(end, end);
+      searchInput.scrollLeft = searchInput.scrollWidth;
     });
   });
 }
 
-createClearButton(qInput);
-
-// Additionally to searching when selecting a new category, we also
-// automatically start a new search request when the user changes a search
-// filter (safesearch, time range or language) (this requires JavaScript
-// though)
-if (
-  settings.search_on_category_select &&
-  // If .search_filters is undefined (invisible) we are on the homepage and
-  // hence don't have to set any listeners
-  document.querySelector(".search_filters")
-) {
-  const safesearchElement = document.getElementById("safesearch");
-  if (safesearchElement) {
-    listen("change", safesearchElement, () => submitIfQuery(qInput));
-  }
-
-  const timeRangeElement = document.getElementById("time_range");
-  if (timeRangeElement) {
-    listen("change", timeRangeElement, () => submitIfQuery(qInput));
-  }
+listen("input", searchInput, () => {
+  searchReset.classList.toggle("empty", searchInput.value.length === 0);
+});
 
-  const languageElement = document.getElementById("language");
-  if (languageElement) {
-    listen("change", languageElement, () => submitIfQuery(qInput));
-  }
-}
+listen("click", searchReset, () => {
+  searchReset.classList.add("empty");
+  searchInput.focus();
+});
 
-const categoryButtons: HTMLButtonElement[] = [
-  ...document.querySelectorAll<HTMLButtonElement>("button.category_button")
-];
 for (const button of categoryButtons) {
   listen("click", button, (event: MouseEvent) => {
     if (event.shiftKey) {
@@ -98,21 +59,34 @@ for (const button of categoryButtons) {
   });
 }
 
-const form: HTMLFormElement | null = document.querySelector<HTMLFormElement>("#search");
-assertElement(form);
+if (document.querySelector("div.search_filters")) {
+  const safesearchElement = document.getElementById("safesearch");
+  if (safesearchElement) {
+    listen("change", safesearchElement, () => searchForm.submit());
+  }
+
+  const timeRangeElement = document.getElementById("time_range");
+  if (timeRangeElement) {
+    listen("change", timeRangeElement, () => searchForm.submit());
+  }
 
-// override form submit action to update the actually selected categories
-listen("submit", form, (event: Event) => {
+  const languageElement = document.getElementById("language");
+  if (languageElement) {
+    listen("change", languageElement, () => searchForm.submit());
+  }
+}
+
+// override searchForm submit event
+listen("submit", searchForm, (event: Event) => {
   event.preventDefault();
 
-  const categoryValuesInput = document.querySelector<HTMLInputElement>("#selected-categories");
-  if (categoryValuesInput) {
-    const categoryValues = categoryButtons
+  if (categoryButtons.length > 0) {
+    const searchCategories = getElement<HTMLInputElement>("selected-categories");
+    searchCategories.value = categoryButtons
       .filter((button) => button.classList.contains("selected"))
-      .map((button) => button.name.replace("category_", ""));
-
-    categoryValuesInput.value = categoryValues.join(",");
+      .map((button) => button.name.replace("category_", ""))
+      .join(",");
   }
 
-  form.submit();
+  searchForm.submit();
 });
diff --git a/client/simple/src/js/pkg/ol.ts b/client/simple/src/js/pkg/ol.ts
deleted file mode 100644
index 28eed3c03..000000000
--- a/client/simple/src/js/pkg/ol.ts
+++ /dev/null
@@ -1,28 +0,0 @@
-// SPDX-License-Identifier: AGPL-3.0-or-later
-
-import { Feature, Map as OlMap, View } from "ol";
-import { createEmpty } from "ol/extent";
-import { GeoJSON } from "ol/format";
-import { Point } from "ol/geom";
-import { Tile as TileLayer, Vector as VectorLayer } from "ol/layer";
-import { fromLonLat } from "ol/proj";
-import { OSM, Vector as VectorSource } from "ol/source";
-import { Circle, Fill, Stroke, Style } from "ol/style";
-
-export {
-  View,
-  OlMap,
-  TileLayer,
-  VectorLayer,
-  OSM,
-  createEmpty,
-  VectorSource,
-  Style,
-  Stroke,
-  Fill,
-  Circle,
-  fromLonLat,
-  GeoJSON,
-  Feature,
-  Point
-};
diff --git a/client/simple/src/js/plugin/Calculator.ts b/client/simple/src/js/plugin/Calculator.ts
new file mode 100644
index 000000000..95196a840
--- /dev/null
+++ b/client/simple/src/js/plugin/Calculator.ts
@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {
+  absDependencies,
+  addDependencies,
+  create,
+  divideDependencies,
+  eDependencies,
+  evaluateDependencies,
+  expDependencies,
+  factorialDependencies,
+  gcdDependencies,
+  lcmDependencies,
+  log1pDependencies,
+  log2Dependencies,
+  log10Dependencies,
+  logDependencies,
+  modDependencies,
+  multiplyDependencies,
+  nthRootDependencies,
+  piDependencies,
+  powDependencies,
+  roundDependencies,
+  signDependencies,
+  sqrtDependencies,
+  subtractDependencies
+} from "mathjs/number";
+import { Plugin } from "../Plugin.ts";
+import { appendAnswerElement } from "../util/appendAnswerElement.ts";
+import { getElement } from "../util/getElement.ts";
+
+/**
+ * Parses and solves mathematical expressions. Can do basic arithmetic and
+ * evaluate some functions.
+ *
+ * @example
+ * "(3 + 5) / 2" = "4"
+ * "e ^ 2 + pi" = "10.530648752520442"
+ * "gcd(48, 18) + lcm(4, 5)" = "26"
+ *
+ * @remarks
+ * Depends on `mathjs` library.
+ */
+export default class Calculator extends Plugin {
+  public constructor() {
+    super("calculator");
+  }
+
+  /**
+   * @remarks
+   * Compare bundle size after adding or removing features.
+   */
+  private static readonly math = create({
+    ...absDependencies,
+    ...addDependencies,
+    ...divideDependencies,
+    ...eDependencies,
+    ...evaluateDependencies,
+    ...expDependencies,
+    ...factorialDependencies,
+    ...gcdDependencies,
+    ...lcmDependencies,
+    ...log10Dependencies,
+    ...log1pDependencies,
+    ...log2Dependencies,
+    ...logDependencies,
+    ...modDependencies,
+    ...multiplyDependencies,
+    ...nthRootDependencies,
+    ...piDependencies,
+    ...powDependencies,
+    ...roundDependencies,
+    ...signDependencies,
+    ...sqrtDependencies,
+    ...subtractDependencies
+  });
+
+  protected async run(): Promise<string | undefined> {
+    const searchInput = getElement<HTMLInputElement>("q");
+    const node = Calculator.math.parse(searchInput.value);
+
+    try {
+      return `${node.toString()} = ${node.evaluate()}`;
+    } catch {
+      // not a compatible math expression
+      return;
+    }
+  }
+
+  protected async post(result: string): Promise<void> {
+    appendAnswerElement(result);
+  }
+}
diff --git a/client/simple/src/js/plugin/InfiniteScroll.ts b/client/simple/src/js/plugin/InfiniteScroll.ts
new file mode 100644
index 000000000..96e57d2f6
--- /dev/null
+++ b/client/simple/src/js/plugin/InfiniteScroll.ts
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import { Plugin } from "../Plugin.ts";
+import { http, settings } from "../toolkit.ts";
+import { assertElement } from "../util/assertElement.ts";
+import { getElement } from "../util/getElement.ts";
+
+/**
+ * Automatically loads the next page when scrolling to bottom of the current page.
+ */
+export default class InfiniteScroll extends Plugin {
+  public constructor() {
+    super("infiniteScroll");
+  }
+
+  protected async run(): Promise<void> {
+    const resultsElement = getElement<HTMLElement>("results");
+
+    const onlyImages: boolean = resultsElement.classList.contains("only_template_images");
+    const observedSelector = "article.result:last-child";
+
+    const spinnerElement = document.createElement("div");
+    spinnerElement.className = "loader";
+
+    const loadNextPage = async (callback: () => void): Promise<void> => {
+      const searchForm = document.querySelector<HTMLFormElement>("#search");
+      assertElement(searchForm);
+
+      const form = document.querySelector<HTMLFormElement>("#pagination form.next_page");
+      assertElement(form);
+
+      const action = searchForm.getAttribute("action");
+      if (!action) {
+        throw new Error("Form action not defined");
+      }
+
+      const paginationElement = document.querySelector<HTMLElement>("#pagination");
+      assertElement(paginationElement);
+
+      paginationElement.replaceChildren(spinnerElement);
+
+      try {
+        const res = await http("POST", action, { body: new FormData(form) });
+        const nextPage = await res.text();
+        if (!nextPage) return;
+
+        const nextPageDoc = new DOMParser().parseFromString(nextPage, "text/html");
+        const articleList = nextPageDoc.querySelectorAll<HTMLElement>("#urls article");
+        const nextPaginationElement = nextPageDoc.querySelector<HTMLElement>("#pagination");
+
+        document.querySelector("#pagination")?.remove();
+
+        const urlsElement = document.querySelector<HTMLElement>("#urls");
+        if (!urlsElement) {
+          throw new Error("URLs element not found");
+        }
+
+        if (articleList.length > 0 && !onlyImages) {
+          // do not add <hr> element when there are only images
+          urlsElement.appendChild(document.createElement("hr"));
+        }
+
+        urlsElement.append(...articleList);
+
+        if (nextPaginationElement) {
+          const results = document.querySelector<HTMLElement>("#results");
+          results?.appendChild(nextPaginationElement);
+          callback();
+        }
+      } catch (error) {
+        console.error("Error loading next page:", error);
+
+        const errorElement = Object.assign(document.createElement("div"), {
+          textContent: settings.translations?.error_loading_next_page ?? "Error loading next page",
+          className: "dialog-error"
+        });
+        errorElement.setAttribute("role", "alert");
+        document.querySelector("#pagination")?.replaceChildren(errorElement);
+      }
+    };
+
+    const intersectionObserveOptions: IntersectionObserverInit = {
+      rootMargin: "320px"
+    };
+
+    const observer: IntersectionObserver = new IntersectionObserver(async (entries: IntersectionObserverEntry[]) => {
+      const [paginationEntry] = entries;
+
+      if (paginationEntry?.isIntersecting) {
+        observer.unobserve(paginationEntry.target);
+
+        await loadNextPage(() => {
+          const nextObservedElement = document.querySelector<HTMLElement>(observedSelector);
+          if (nextObservedElement) {
+            observer.observe(nextObservedElement);
+          }
+        });
+      }
+    }, intersectionObserveOptions);
+
+    const initialObservedElement: HTMLElement | null = document.querySelector<HTMLElement>(observedSelector);
+    if (initialObservedElement) {
+      observer.observe(initialObservedElement);
+    }
+  }
+
+  protected async post(): Promise<void> {
+    // noop
+  }
+}
diff --git a/client/simple/src/js/plugin/MapView.ts b/client/simple/src/js/plugin/MapView.ts
new file mode 100644
index 000000000..b1e199a57
--- /dev/null
+++ b/client/simple/src/js/plugin/MapView.ts
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import "ol/ol.css?inline";
+import { Feature, Map as OlMap, View } from "ol";
+import { GeoJSON } from "ol/format";
+import { Point } from "ol/geom";
+import { Tile as TileLayer, Vector as VectorLayer } from "ol/layer";
+import { fromLonLat } from "ol/proj";
+import { OSM, Vector as VectorSource } from "ol/source";
+import { Circle, Fill, Stroke, Style } from "ol/style";
+import { Plugin } from "../Plugin.ts";
+
+/**
+ * MapView
+ */
+export default class MapView extends Plugin {
+  private readonly map: HTMLElement;
+
+  public constructor(map: HTMLElement) {
+    super("mapView");
+
+    this.map = map;
+  }
+
+  protected async run(): Promise<void> {
+    const { leafletTarget: target, mapLon, mapLat, mapGeojson } = this.map.dataset;
+
+    const lon = Number.parseFloat(mapLon || "0");
+    const lat = Number.parseFloat(mapLat || "0");
+    const view = new View({ maxZoom: 16, enableRotation: false });
+    const map = new OlMap({
+      target: target,
+      layers: [new TileLayer({ source: new OSM({ maxZoom: 16 }) })],
+      view: view
+    });
+
+    try {
+      const markerSource = new VectorSource({
+        features: [
+          new Feature({
+            geometry: new Point(fromLonLat([lon, lat]))
+          })
+        ]
+      });
+
+      const markerLayer = new VectorLayer({
+        source: markerSource,
+        style: new Style({
+          image: new Circle({
+            radius: 6,
+            fill: new Fill({ color: "#3050ff" })
+          })
+        })
+      });
+
+      map.addLayer(markerLayer);
+    } catch (error) {
+      console.error("Failed to create marker layer:", error);
+    }
+
+    if (mapGeojson) {
+      try {
+        const geoSource = new VectorSource({
+          features: new GeoJSON().readFeatures(JSON.parse(mapGeojson), {
+            dataProjection: "EPSG:4326",
+            featureProjection: "EPSG:3857"
+          })
+        });
+
+        const geoLayer = new VectorLayer({
+          source: geoSource,
+          style: new Style({
+            stroke: new Stroke({ color: "#3050ff", width: 2 }),
+            fill: new Fill({ color: "#3050ff33" })
+          })
+        });
+
+        map.addLayer(geoLayer);
+
+        view.fit(geoSource.getExtent(), { padding: [20, 20, 20, 20] });
+      } catch (error) {
+        console.error("Failed to create GeoJSON layer:", error);
+      }
+    }
+  }
+
+  protected async post(): Promise<void> {
+    // noop
+  }
+}
diff --git a/client/simple/src/js/router.ts b/client/simple/src/js/router.ts
new file mode 100644
index 000000000..24abb64c3
--- /dev/null
+++ b/client/simple/src/js/router.ts
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import { load } from "./loader.ts";
+import { Endpoints, endpoint, listen, ready, settings } from "./toolkit.ts";
+
+ready(() => {
+  document.documentElement.classList.remove("no-js");
+  document.documentElement.classList.add("js");
+
+  listen("click", ".close", function (this: HTMLElement) {
+    (this.parentNode as HTMLElement)?.classList.add("invisible");
+  });
+
+  listen("click", ".searxng_init_map", async function (this: HTMLElement, event: Event) {
+    event.preventDefault();
+    this.classList.remove("searxng_init_map");
+
+    load(() => import("./plugin/MapView.ts").then(({ default: Plugin }) => new Plugin(this)), {
+      on: "endpoint",
+      where: [Endpoints.results]
+    });
+  });
+
+  if (settings.plugins?.includes("infiniteScroll")) {
+    load(() => import("./plugin/InfiniteScroll.ts").then(({ default: Plugin }) => new Plugin()), {
+      on: "endpoint",
+      where: [Endpoints.results]
+    });
+  }
+
+  if (settings.plugins?.includes("calculator")) {
+    load(() => import("./plugin/Calculator.ts").then(({ default: Plugin }) => new Plugin()), {
+      on: "endpoint",
+      where: [Endpoints.results]
+    });
+  }
+});
+
+ready(
+  () => {
+    void import("./main/keyboard.ts");
+    void import("./main/search.ts");
+
+    if (settings.autocomplete) {
+      void import("./main/autocomplete.ts");
+    }
+  },
+  { on: [endpoint === Endpoints.index] }
+);
+
+ready(
+  () => {
+    void import("./main/keyboard.ts");
+    void import("./main/results.ts");
+    void import("./main/search.ts");
+
+    if (settings.autocomplete) {
+      void import("./main/autocomplete.ts");
+    }
+  },
+  { on: [endpoint === Endpoints.results] }
+);
+
+ready(
+  () => {
+    void import("./main/preferences.ts");
+  },
+  { on: [endpoint === Endpoints.preferences] }
+);
diff --git a/client/simple/src/js/core/toolkit.ts b/client/simple/src/js/toolkit.ts
index d80167aa5..2eaf1d02c 100644
--- a/client/simple/src/js/core/toolkit.ts
+++ b/client/simple/src/js/toolkit.ts
@@ -1,16 +1,16 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
-import type { KeyBindingLayout } from "../main/keyboard.ts";
+import type { KeyBindingLayout } from "./main/keyboard.ts";
 
 // synced with searx/webapp.py get_client_settings
 type Settings = {
+  plugins?: string[];
   advanced_search?: boolean;
   autocomplete?: string;
   autocomplete_min?: number;
   doi_resolver?: string;
   favicon_resolver?: string;
   hotkeys?: KeyBindingLayout;
-  infinite_scroll?: boolean;
   method?: "GET" | "POST";
   query_in_title?: boolean;
   results_on_new_tab?: boolean;
@@ -32,8 +32,6 @@ type ReadyOptions = {
   on?: (boolean | undefined)[];
 };
 
-type AssertElement = (element?: HTMLElement | null) => asserts element is HTMLElement;
-
 export type EndpointsKeys = keyof typeof Endpoints;
 
 export const Endpoints = {
@@ -73,12 +71,6 @@ const getSettings = (): Settings => {
   }
 };
 
-export const assertElement: AssertElement = (element?: HTMLElement | null): asserts element is HTMLElement => {
-  if (!element) {
-    throw new Error("Bad assertion: DOM element not found");
-  }
-};
-
 export const http = async (method: string, url: string | URL, options?: HTTPOptions): Promise<Response> => {
   const controller = new AbortController();
   const timeoutId = setTimeout(() => controller.abort(), options?.timeout ?? 30_000);
diff --git a/client/simple/src/js/util/appendAnswerElement.ts b/client/simple/src/js/util/appendAnswerElement.ts
new file mode 100644
index 000000000..d21db3f48
--- /dev/null
+++ b/client/simple/src/js/util/appendAnswerElement.ts
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import { getElement } from "./getElement.ts";
+
+export const appendAnswerElement = (element: HTMLElement | string | number): void => {
+  const results = getElement<HTMLDivElement>("results");
+
+  // ./searx/templates/elements/answers.html
+  let answers = getElement<HTMLDivElement>("answers", { assert: false });
+  if (!answers) {
+    // what is this?
+    const answersTitle = document.createElement("h4");
+    answersTitle.setAttribute("class", "title");
+    answersTitle.setAttribute("id", "answers-title");
+    answersTitle.textContent = "Answers : ";
+
+    answers = document.createElement("div");
+    answers.setAttribute("id", "answers");
+    answers.setAttribute("role", "complementary");
+    answers.setAttribute("aria-labelledby", "answers-title");
+    answers.appendChild(answersTitle);
+  }
+
+  if (!(element instanceof HTMLElement)) {
+    const span = document.createElement("span");
+    span.innerHTML = element.toString();
+    // biome-ignore lint/style/noParameterAssign: TODO
+    element = span;
+  }
+
+  answers.appendChild(element);
+
+  results.insertAdjacentElement("afterbegin", answers);
+};
diff --git a/client/simple/src/js/util/assertElement.ts b/client/simple/src/js/util/assertElement.ts
new file mode 100644
index 000000000..a362fcf8f
--- /dev/null
+++ b/client/simple/src/js/util/assertElement.ts
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+type AssertElement = <T>(element?: T | null) => asserts element is T;
+export const assertElement: AssertElement = <T>(element?: T | null): asserts element is T => {
+  if (!element) {
+    throw new Error("DOM element not found");
+  }
+};
diff --git a/client/simple/src/js/util/getElement.ts b/client/simple/src/js/util/getElement.ts
new file mode 100644
index 000000000..cfb2caf4e
--- /dev/null
+++ b/client/simple/src/js/util/getElement.ts
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import { assertElement } from "./assertElement.ts";
+
+type Options = {
+  assert?: boolean;
+};
+
+export function getElement<T>(id: string, options?: { assert: true }): T;
+export function getElement<T>(id: string, options?: { assert: false }): T | null;
+export function getElement<T>(id: string, options: Options = {}): T | null {
+  options.assert ??= true;
+
+  const element = document.getElementById(id) as T | null;
+
+  if (options.assert) {
+    assertElement(element);
+  }
+
+  return element;
+}