refactor: use const instead of let for variable declarations (#4196)

This replaces `let` with `const` for variable declarations where it was
possible. Using `const` [is considered best
practice](https://www.xjavascript.com/blog/in-javascript-why-should-i-usually-prefer-const-to-let/#5-best-practices-const-first-let-second).

I have enabled the corresponding ESLint rule and let the ESLint auto-fix
the "wrong" usages of `let`.

js/app.js

@@ -65,7 +65,7 @@ process.on("uncaughtException", function (err) {
  * @class
  */
 function App () {
-	let nodeHelpers = [];
+	const nodeHelpers = [];
 	let httpServer;
 	let defaultModules;
 	let env;
@@ -118,7 +118,7 @@ function App () {
 				Log.error(`Error when loading ${moduleName}:`, e.message);
 				return;
 			}
-			let m = new Module();
+			const m = new Module();
 
 			if (m.requiresVersion) {
 				Log.log(`Check MagicMirror² version for node helper '${moduleName}' - Minimum version: ${m.requiresVersion} - Current version: ${global.version}`);
@@ -146,7 +146,7 @@ function App () {
 	async function loadModules (modules) {
 		Log.log("Loading module helpers ...");
 
-		for (let module of modules) {
+		for (const module of modules) {
 			await loadModule(module);
 		}
 
@@ -211,7 +211,7 @@ function App () {
 			// get the used module positions
 			Utils.getModulePositions();
 
-			let modules = [];
+			const modules = [];
 			for (const module of config.modules) {
 				if (module.disabled) continue;
 				if (module.module) {
@@ -237,7 +237,7 @@ function App () {
 			Log.log("Server started ...");
 
 			const nodePromises = [];
-			for (let nodeHelper of nodeHelpers) {
+			for (const nodeHelper of nodeHelpers) {
 				nodeHelper.setExpressApp(app);
 				nodeHelper.setSocketIO(io);
 
@@ -284,7 +284,7 @@ function App () {
 	 */
 	this.stop = async function () {
 		const nodePromises = [];
-		for (let nodeHelper of nodeHelpers) {
+		for (const nodeHelper of nodeHelpers) {
 			try {
 				if (typeof nodeHelper.stop === "function") {
 					nodePromises.push(nodeHelper.stop());

js/electron.js

@@ -45,7 +45,7 @@ function createWindow () {
 	}
 
 	applyElectronSwitches(app.commandLine, config.electronSwitches);
-	let electronOptionsDefaults = {
+	const electronOptionsDefaults = {
 		width: electronSize.width,
 		height: electronSize.height,
 		icon: "favicon.svg",
@@ -100,7 +100,7 @@ function createWindow () {
 		prefix = "http://";
 	}
 
-	let address = (config.address === void 0) | (config.address === "") | (config.address === "0.0.0.0") | (config.address === "::") ? (config.address = "localhost") : config.address;
+	const address = (config.address === void 0) | (config.address === "") | (config.address === "0.0.0.0") | (config.address === "::") ? (config.address = "localhost") : config.address;
 	const port = process.env.MM_PORT || config.port;
 	mainWindow.loadURL(`${prefix}${address}:${port}`);
 

js/main.js

@@ -196,7 +196,6 @@ function moduleNeedsUpdate (module, newHeader, newContent) {
 	const headerWrapper = moduleWrapper.getElementsByClassName("module-header");
 
 	let headerNeedsUpdate = false;
-	let contentNeedsUpdate;
 
 	if (headerWrapper.length > 0) {
 		headerNeedsUpdate = newHeader !== headerWrapper[0].innerHTML;
@@ -204,7 +203,7 @@ function moduleNeedsUpdate (module, newHeader, newContent) {
 
 	const tempContentWrapper = document.createElement("div");
 	tempContentWrapper.appendChild(newContent);
-	contentNeedsUpdate = tempContentWrapper.innerHTML !== contentWrapper[0].innerHTML;
+	const contentNeedsUpdate = tempContentWrapper.innerHTML !== contentWrapper[0].innerHTML;
 
 	return headerNeedsUpdate || contentNeedsUpdate;
 }

js/module.js

@@ -520,7 +520,7 @@ export function cmpVersions (a, b) {
 	const l = Math.min(segmentsA.length, segmentsB.length);
 
 	for (let i = 0; i < l; i++) {
-		let diff = parseInt(segmentsA[i], 10) - parseInt(segmentsB[i], 10);
+		const diff = parseInt(segmentsA[i], 10) - parseInt(segmentsB[i], 10);
 		if (diff) {
 			return diff;
 		}

js/server.js

@@ -98,7 +98,7 @@ function Server (configObj) {
 				});
 			}
 
-			let directories = ["/config", "/css", "/favicon.svg", "/defaultmodules", "/modules", "/node_modules/animate.css", "/node_modules/@fontsource", "/node_modules/@fortawesome", "/node_modules/suncalc", "/translations", "/tests/configs", "/tests/mocks"];
+			const directories = ["/config", "/css", "/favicon.svg", "/defaultmodules", "/modules", "/node_modules/animate.css", "/node_modules/@fontsource", "/node_modules/@fortawesome", "/node_modules/suncalc", "/translations", "/tests/configs", "/tests/mocks"];
 			for (const value of Object.values(vendor)) {
 				const dirArr = value.split("/");
 				if (dirArr[0] === "node_modules") directories.push(`/${dirArr[0]}/${dirArr[1]}`);

js/systeminformation.js

@@ -25,7 +25,7 @@ const logSystemInformation = async () => {
 		const freeRam = (os.freemem() / 1024 / 1024).toFixed(2);
 		const usedRam = ((os.totalmem() - os.freemem()) / 1024 / 1024).toFixed(2);
 
-		let systemDataString = [
+		const systemDataString = [
 			"\n####  System Information  ####",
 			`- MM:       version: v${mmVersion}${mmGitHash ? `; git: ${mmGitHash}` : ""}${mmGitBranch ? `; branch: ${mmGitBranch}` : ""}`,
 			`- SYSTEM:   manufacturer: ${system.manufacturer}; model: ${system.model}; virtual: ${system.virtual}`,

js/translator.js

@@ -117,7 +117,7 @@ const Translator = (function () {
 		 * The first language defined in translations.js will be used.
 		 */
 		async loadCoreTranslationsFallback () {
-			let first = Object.keys(translations)[0];
+			const first = Object.keys(translations)[0];
 			if (first) {
 				Log.log(`[translator] Loading core translation fallback file: ${translations[first]}`);
 				this.coreTranslationsFallback = await loadJSON(translations[first]);

js/utils.js

@@ -110,7 +110,7 @@ const loadConfig = () => {
 	// For this check proposed to TestSuite
 	// https://forum.magicmirror.builders/topic/1456/test-suite-for-magicmirror/8
 	const configFilename = getConfigFilePath();
-	let templateFile = `${configFilename}.template`;
+	const templateFile = `${configFilename}.template`;
 
 	// check if templateFile exists
 	try {
@@ -133,7 +133,7 @@ const loadConfig = () => {
 
 	// Load config.js and catch errors if not accessible
 	try {
-		let configContent = fs.readFileSync(configFilename, "utf-8");
+		const configContent = fs.readFileSync(configFilename, "utf-8");
 		const hideConfigSecrets = configContent.match(/^\s*hideConfigSecrets: true.*$/m);
 		let configContentFull = configContent;
 		let configContentRedacted = hideConfigSecrets ? configContent : undefined;