diff --git a/code/html/src/core.mjs b/code/html/src/core.mjs
index fbc8434a..7a36c3f7 100644
--- a/code/html/src/core.mjs
+++ b/code/html/src/core.mjs
@@ -1,3 +1,6 @@
+/**
+ * @param {string[]} rules
+ */
 export function styleInject(rules) {
     if (!rules.length) {
         return;
@@ -7,23 +10,30 @@ export function styleInject(rules) {
     style.setAttribute("type", "text/css");
     document.head.appendChild(style);
 
-    let pos = style.sheet.cssRules.length;
+    const sheet = style.sheet;
+    if (!sheet) {
+        return;
+    }
+
+    let pos = sheet.cssRules.length;
     for (let rule of rules) {
         style.sheet.insertRule(rule, pos++);
     }
 }
 
+/**
+ * @param {string} selector
+ * @param {boolean} value
+ */
 export function styleVisible(selector, value) {
     return `${selector} { content-visibility: ${value ? "visible": "hidden"}; }`
 }
 
 /**
- * @param {number} ms
+ * @param {number} timeout
  */
-export function pageReloadIn(ms) {
-    setTimeout(() => {
-        window.location.reload();
-    }, parseInt(ms, 10));
+export function pageReloadIn(timeout) {
+    setTimeout(window.location.reload, timeout);
 }
 
 /**
@@ -41,11 +51,9 @@ export function moreElem(container) {
         });
 }
 
-export function toggleMenu(event) {
-    event.preventDefault();
-    event.target.parentElement.classList.toggle("active");
-}
-
+/**
+ * @param {string} name
+ */
 export function showPanelByName(name) {
     // only a single panel is shown on the 'layout'
     const target = document.getElementById(`panel-${name}`);
@@ -53,13 +61,20 @@ export function showPanelByName(name) {
         return;
     }
 
-    for (const panel of document.querySelectorAll(".panel")) {
+    for (const panel of document.getElementsByClassName("panel")) {
+        if (!(panel instanceof HTMLElement)) {
+            continue;
+        }
+
         panel.style.display = "none";
     }
+
     target.style.display = "revert";
 
     const layout = document.getElementById("layout");
-    layout.classList.remove("active");
+    if (layout) {
+        layout.classList.remove("active");
+    }
 
     // TODO: sometimes, switching view causes us to scroll past
     // the header (e.g. emon ratios panel on small screen)
@@ -70,32 +85,43 @@ export function showPanelByName(name) {
     }
 }
 
-export function showPanel(event) {
+/**
+ * @param {Event} event
+ */
+export function onPanelTargetClick(event) {
     event.preventDefault();
-    showPanelByName(event.target.dataset["panel"]);
-}
 
-export function randomString(length, args) {
-    if (typeof args === "undefined") {
-        args = {
-            lowercase: true,
-            uppercase: true,
-            numbers: true,
-            special: true
-        }
+    const target = event.target;
+    if (!(target instanceof HTMLElement)) {
+        return;
     }
 
+    const name = target.dataset["panel"];
+    if (name) {
+        showPanelByName(name);
+    }
+}
+
+/**
+ * @typedef {{hex?: boolean, lowercase?: boolean, numbers?: boolean, special?: boolean, uppercase?: boolean}} RandomStringOptions
+ *
+ * @param {number} length
+ * @param {RandomStringOptions} options
+ */
+export function randomString(length, {hex = false, lowercase = true, numbers = true, special = false, uppercase = true} = {}) {
     let mask = "";
-    if (args.lowercase) { mask += "abcdefghijklmnopqrstuvwxyz"; }
-    if (args.uppercase) { mask += "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; }
-    if (args.numbers || args.hex) { mask += "0123456789"; }
-    if (args.hex) { mask += "ABCDEF"; }
-    if (args.special) { mask += "~`!@#$%^&*()_+-={}[]:\";'<>?,./|\\"; }
+    if (lowercase || hex) { mask += "abcdef"; }
+    if (lowercase) { mask += "ghijklmnopqrstuvwxyz"; }
+    if (uppercase || hex) { mask += "ABCDEF"; }
+    if (uppercase) { mask += "GHIJKLMNOPQRSTUVWXYZ"; }
+    if (numbers || hex) { mask += "0123456789"; }
+    if (special) { mask += "~`!@#$%^&*()_+-={}[]:\";'<>?,./|\\"; }
 
-    let source = new Uint32Array(length);
-    let result = new Array(length);
+    const source = new Uint32Array(length);
+    const result = new Array(length);
 
-    window.crypto.getRandomValues(source)
+    window.crypto
+        .getRandomValues(source)
         .forEach((value, i) => {
             result[i] = mask[value % mask.length];
         });
diff --git a/code/html/src/index.mjs b/code/html/src/index.mjs
index e5d7320f..44e16869 100644
--- a/code/html/src/index.mjs
+++ b/code/html/src/index.mjs
@@ -6,21 +6,18 @@ window.onerror = notifyError;
 import {
     pageReloadIn,
     randomString,
-    showPanel,
+    onPanelTargetClick,
     styleInject,
 } from './core.mjs';
 
 import { validatePassword, validateFormsPasswords } from './validate.mjs';
 
-import {
-    askAndCallAction,
-    askAndCallReboot,
-    askAndCallReconnect,
-} from './question.mjs';
+import { askAndCall } from './question.mjs';
 
 import {
     init as initSettings,
     applySettings,
+    askSaveSettings,
     getData,
     setChangedElement,
     updateVariables,
@@ -29,7 +26,11 @@ import {
 
 import { init as initWiFi } from './wifi.mjs';
 import { init as initGpio } from './gpio.mjs';
-import { init as initConnection, connect } from './connection.mjs';
+import {
+    init as initConnection,
+    connect,
+    sendAction,
+} from './connection.mjs';
 
 import { init as initApi } from './api.mjs';
 import { init as initCurtain } from './curtain.mjs';
@@ -221,8 +222,52 @@ function keepTime() {
     }
 }
 
+/** @import { QuestionWrapper } from './question.mjs' */
+
+/** @type {QuestionWrapper} */
+function askDisconnect(ask) {
+    return ask("Are you sure you want to disconnect from the current WiFi network?");
+}
+
+/** @type {QuestionWrapper} */
+function askReboot(ask) {
+    return ask("Are you sure you want to reboot the device?");
+}
+
+function askAndCallReconnect() {
+    askAndCall([askSaveSettings, askDisconnect], () => {
+        sendAction("reconnect");
+    });
+}
+
+function askAndCallReboot() {
+    askAndCall([askSaveSettings, askReboot], () => {
+        sendAction("reboot");
+    });
+}
+
+/** @param {Event} event */
+function askAndCallSimpleAction(event) {
+    const target = event.target;
+    if (!(target instanceof HTMLButtonElement)) {
+        return;
+    }
+
+    /** @type {QuestionWrapper} */
+    const wrapper =
+        (ask) => ask(`Confirm the action: "${target.textContent}"`);
+
+    askAndCall([wrapper], () => {
+        sendAction(target.name);
+    });
+}
+
 /**
- * @returns {import("./settings.mjs").KeyValueListeners}
+ * @import { KeyValueListeners } from './settings.mjs'
+ */
+
+/**
+ * @returns {KeyValueListeners}
  */
 function listeners() {
     return {
@@ -298,17 +343,32 @@ function initSetupPassword(form) {
  * @param {Event} event
  * @returns {any}
  */
-function toggleMenu(event) {
+function onMenuLinkClick(event) {
     event.preventDefault();
-    /** @type {HTMLElement} */(event.target).parentElement?.classList.toggle("active");
+
+    const target = event.target;
+    if (!(target instanceof HTMLElement)) {
+        return;
+    }
+
+    if (target?.parentElement) {
+        target.parentElement.classList.toggle("active");
+    }
 }
 
 /**
  * @param {Event} event
  */
-function toggleVisiblePassword(event) {
-    const target = /** @type {HTMLSpanElement} */(event.target);
-    const input = /** @type {HTMLInputElement} */(target.previousElementSibling);
+function onPasswordRevealClick(event) {
+    const target = event.target;
+    if (!(target instanceof HTMLElement)) {
+        return;
+    }
+
+    const input = target.previousElementSibling;
+    if (!(input instanceof HTMLInputElement)) {
+        return;
+    }
 
     if (input.type === "password") {
         input.type = "text";
@@ -348,15 +408,15 @@ function init() {
 
     document.querySelectorAll(".password-reveal")
         .forEach((elem) => {
-            elem.addEventListener("click", toggleVisiblePassword);
+            elem.addEventListener("click", onPasswordRevealClick);
         });
 
     // Sidebar menu & buttons
     document.querySelector(".menu-link")
-        ?.addEventListener("click", toggleMenu);
+        ?.addEventListener("click", onMenuLinkClick);
     document.querySelectorAll(".pure-menu-link")
         .forEach((elem) => {
-            elem.addEventListener("click", showPanel);
+            elem.addEventListener("click", onPanelTargetClick);
         });
 
     document.querySelector(".button-reconnect")
@@ -369,7 +429,7 @@ function init() {
     // Generic action sender
     document.querySelectorAll(".button-simple-action")
         .forEach((elem) => {
-            elem.addEventListener("click", askAndCallAction);
+            elem.addEventListener("click", askAndCallSimpleAction);
         });
 
     variableListeners(listeners());
diff --git a/code/html/src/question.mjs b/code/html/src/question.mjs
index d534abd8..90fb1179 100644
--- a/code/html/src/question.mjs
+++ b/code/html/src/question.mjs
@@ -1,22 +1,15 @@
-import { pendingChanges } from './settings.mjs';
-import { sendAction } from './connection.mjs';
+/**
+ * @typedef {function(string): boolean} Question
+ */
 
-export function askSaveSettings(ask) {
-    if (pendingChanges()) {
-        return ask("There are pending changes to the settings, continue the operation without saving?");
-    }
-
-    return true;
-}
-
-export function askDisconnect(ask) {
-    return ask("Are you sure you want to disconnect from the current WiFi network?");
-}
-
-export function askReboot(ask) {
-    return ask("Are you sure you want to reboot the device?");
-}
+/**
+ * @typedef {function(Question): boolean} QuestionWrapper
+ */
 
+/**
+ * @param {QuestionWrapper[]} questions
+ * @param {function(): void} callback
+ */
 export function askAndCall(questions, callback) {
     for (let question of questions) {
         if (!question(window.confirm)) {
@@ -26,22 +19,3 @@ export function askAndCall(questions, callback) {
 
     callback();
 }
-
-export function askAndCallReconnect() {
-    askAndCall([askSaveSettings, askDisconnect], () => {
-        sendAction("reconnect");
-    });
-}
-
-export function askAndCallReboot() {
-    askAndCall([askSaveSettings, askReboot], () => {
-        sendAction("reboot");
-    });
-}
-
-export function askAndCallAction(event) {
-    askAndCall([(ask) => ask(`Confirm the action: "${event.target.textContent}"`)], () => {
-        sendAction(event.target.name);
-    });
-}
-
diff --git a/code/html/src/sensor.mjs b/code/html/src/sensor.mjs
index 96db50e6..70263bc5 100644
--- a/code/html/src/sensor.mjs
+++ b/code/html/src/sensor.mjs
@@ -8,7 +8,7 @@ import {
 } from './template.mjs';
 
 import {
-    showPanel,
+    onPanelTargetClick,
     showPanelByName,
     styleInject,
     styleVisible,
@@ -358,7 +358,7 @@ export function init() {
     variableListeners(listeners());
 
     document.querySelector(".button-emon-expected")
-        .addEventListener("click", showPanel);
+        .addEventListener("click", onPanelTargetClick);
     document.querySelector(".button-emon-expected-calculate")
         .addEventListener("click", emonCalculateRatios);
     document.querySelector(".button-emon-expected-apply")
diff --git a/code/html/src/settings.mjs b/code/html/src/settings.mjs
index ac03271a..c35b622f 100644
--- a/code/html/src/settings.mjs
+++ b/code/html/src/settings.mjs
@@ -1195,6 +1195,20 @@ export function pendingChanges() {
     return Settings.counters.changed > 0;
 }
 
+/**
+ * TODO https://github.com/microsoft/TypeScript/issues/58969 ? at-import becomes 'unused' for some reason
+ * @typedef {import("./question.mjs").QuestionWrapper} QuestionWrapper
+ */
+
+/** @type {QuestionWrapper} */
+export function askSaveSettings(ask) {
+    if (pendingChanges()) {
+        return ask("There are pending changes to the settings, continue the operation without saving?");
+    }
+
+    return true;
+}
+
 /** @returns {KeyValueListeners} */
 function listeners() {
     return {
@@ -1249,7 +1263,7 @@ export function init() {
 
     document.querySelectorAll(".button-add-settings-group")
         .forEach((elem) => {
-            elem.addEventListener("click", groupSettingsAdd);
+            elem.addEventListener("click", onGroupSettingsAddClick);
         });
 
     // No group handler should be registered after this point, since we depend on the order
diff --git a/code/html/src/thermostat.mjs b/code/html/src/thermostat.mjs
index 62c4186b..c678d2e9 100644
--- a/code/html/src/thermostat.mjs
+++ b/code/html/src/thermostat.mjs
@@ -1,4 +1,5 @@
-import { askAndCall, askSaveSettings } from './question.mjs';
+import { askAndCall } from './question.mjs';
+import { askSaveSettings } from './settings.mjs';
 import { sendAction } from './connection.mjs';
 
 function checkTempRange(event) {