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`.

Author: KristjanESPERANTO

config/config.js.sample

@@ -8,7 +8,7 @@
  * which will be converted to `config.js` while starting. For more information
  * see https://docs.magicmirror.builders/configuration/introduction.html#enviromnent-variables
  */
-let config = {
+const config = {
 	address: "localhost",	// Address to listen on, can be:
 							// - "localhost", "127.0.0.1", "::1" to listen on loopback interface
 							// - another specific IPv4/6 to listen on a specific interface

defaultmodules/alert/notificationFx.js

@@ -20,7 +20,7 @@
 	 * @returns {object} The merged object
 	 */
 	function extend (a, b) {
-		for (let key in b) {
+		for (const key in b) {
 			if (b.hasOwnProperty(key)) {
 				a[key] = b[key];
 			}

defaultmodules/calendar/calendar.js

@@ -215,7 +215,7 @@ Module.register("calendar", {
 				return;
 			}
 		} else if (notification === "CALENDAR_ERROR") {
-			let error_message = this.translate(payload.error_type);
+			const error_message = this.translate(payload.error_type);
 			this.error = this.translate("MODULE_CONFIG_ERROR", { MODULE_NAME: this.name, ERROR: error_message });
 			this.loaded = true;
 		}
@@ -350,8 +350,8 @@ Module.register("calendar", {
 
 			// Color events if custom color or eventClass are specified, transform title if required
 			if (this.config.customEvents.length > 0) {
-				for (let ev in this.config.customEvents) {
-					let needle = new RegExp(this.config.customEvents[ev].keyword, "gi");
+				for (const ev in this.config.customEvents) {
+					const needle = new RegExp(this.config.customEvents[ev].keyword, "gi");
 					if (needle.test(event.title)) {
 						if (typeof this.config.customEvents[ev].transform === "object") {
 							transformedTitle = CalendarUtils.titleTransform(transformedTitle, [this.config.customEvents[ev].transform]);
@@ -471,16 +471,16 @@ Module.register("calendar", {
 	 * @returns {object[]} Array with events.
 	 */
 	createEventList (limitNumberOfEntries) {
-		let now = moment();
-		let future = now.clone().startOf("day").add(this.config.maximumNumberOfDays, "days");
+		const now = moment();
+		const future = now.clone().startOf("day").add(this.config.maximumNumberOfDays, "days");
 
 		let events = [];
 
 		for (const calendarUrl in this.calendarData) {
 			const calendar = this.calendarData[calendarUrl].events;
-			let remainingEntries = this.maximumEntriesForUrl(calendarUrl);
-			let maxPastDaysCompare = now.clone().subtract(this.maximumPastDaysForUrl(calendarUrl), "days");
-			let by_url_calevents = [];
+			const remainingEntries = this.maximumEntriesForUrl(calendarUrl);
+			const maxPastDaysCompare = now.clone().subtract(this.maximumPastDaysForUrl(calendarUrl), "days");
+			const by_url_calevents = [];
 			for (const e in calendar) {
 				const event = JSON.parse(JSON.stringify(calendar[e])); // clone object
 				const eventStartDateMoment = this.timestampToMoment(event.startDate);
@@ -541,7 +541,7 @@ Module.register("calendar", {
 					event.tomorrow = this.timestampToMoment(event.startDate).isSame(now.clone().add(1, "days"), "d");
 					splitEvents.push(event);
 
-					for (let splitEvent of splitEvents) {
+					for (const splitEvent of splitEvents) {
 						if (this.timestampToMoment(splitEvent.endDate).isAfter(now) && this.timestampToMoment(splitEvent.endDate).isSameOrBefore(future)) {
 							by_url_calevents.push(splitEvent);
 						}
@@ -579,7 +579,7 @@ Module.register("calendar", {
 			// Group all events by date, events on the same date will be in a list with the key being the date.
 			const eventsByDate = Object.groupBy(events, (ev) => this.timestampToMoment(ev.startDate).format("YYYY-MM-DD"));
 			const newEvents = [];
-			let currentDate = moment();
+			const currentDate = moment();
 			let daysCollected = 0;
 
 			while (daysCollected < this.config.limitDays) {
@@ -650,9 +650,9 @@ Module.register("calendar", {
 		}
 
 		// If custom symbol is set, replace event symbol
-		for (let ev of this.config.customEvents) {
+		for (const ev of this.config.customEvents) {
 			if (typeof ev.symbol !== "undefined" && ev.symbol !== "") {
-				let needle = new RegExp(ev.keyword, "gi");
+				const needle = new RegExp(ev.keyword, "gi");
 				if (needle.test(event.title)) {
 					// Get the default prefix for this class name and add to the custom symbol provided
 					const className = this.getCalendarProperty(event.url, "symbolClassName", this.config.defaultSymbolClassName);
@@ -988,7 +988,7 @@ Module.register("calendar", {
 		if (property === "symbol" || property === "recurringSymbol" || property === "fullDaySymbol") {
 			const className = this.getCalendarProperty(url, "symbolClassName", this.config.defaultSymbolClassName);
 			if (p instanceof Array) {
-				let t = [];
+				const t = [];
 				p.forEach((n) => { t.push(className + n); });
 				p = t;
 			}

defaultmodules/calendar/calendarutils.js

@@ -95,11 +95,11 @@ const CalendarUtils = {
 	 */
 	titleTransform (title, titleReplace) {
 		let transformedTitle = title;
-		for (let tr in titleReplace) {
-			let transform = titleReplace[tr];
+		for (const tr in titleReplace) {
+			const transform = titleReplace[tr];
 			if (typeof transform === "object") {
 				if (typeof transform.search !== "undefined" && transform.search !== "" && typeof transform.replace !== "undefined") {
-					let regParts = transform.search.match(/^\/(.+)\/([gim]*)$/);
+					const regParts = transform.search.match(/^\/(.+)\/([gim]*)$/);
 					let needle = new RegExp(transform.search, "g");
 					if (regParts) {
 						// the parsed pattern is a regexp with flags.
@@ -110,8 +110,8 @@ const CalendarUtils = {
 					if (typeof transform.yearmatchgroup !== "undefined" && transform.yearmatchgroup !== "") {
 						const yearmatch = [...title.matchAll(needle)];
 						if (yearmatch[0].length >= transform.yearmatchgroup + 1 && yearmatch[0][transform.yearmatchgroup] * 1 >= 1900) {
-							let calcage = new Date().getFullYear() - yearmatch[0][transform.yearmatchgroup] * 1;
-							let searchstr = `$${transform.yearmatchgroup}`;
+							const calcage = new Date().getFullYear() - yearmatch[0][transform.yearmatchgroup] * 1;
+							const searchstr = `$${transform.yearmatchgroup}`;
 							replacement = replacement.replace(searchstr, calcage);
 						}
 					}

defaultmodules/compliments/compliments.js

@@ -63,7 +63,7 @@ Module.register("compliments", {
 		}
 		let minute_sync_delay = 1;
 		// loop thru all the configured when events
-		for (let m of Object.keys(this.config.compliments)) {
+		for (const m of Object.keys(this.config.compliments)) {
 			// if it is a cron entry
 			if (this.isCronEntry(m)) {
 				// we need to synch our interval cycle to the minute
@@ -165,14 +165,14 @@ Module.register("compliments", {
 		Array.prototype.push.apply(compliments, this.config.compliments.anytime);
 
 		// get the list of just date entry keys
-		let temp_list = Object.keys(this.config.compliments).filter((k) => {
+		const temp_list = Object.keys(this.config.compliments).filter((k) => {
 			if (this.pre_defined_types.includes(k)) return false;
 			else return true;
 		});
 
-		let date_compliments = [];
+		const date_compliments = [];
 		// Add compliments for special day/times
-		for (let entry of temp_list) {
+		for (const entry of temp_list) {
 			// check if this could be a cron type entry
 			if (this.isCronEntry(entry)) {
 				// make sure the regex is valid

defaultmodules/newsfeed/newsfeed.js

@@ -212,7 +212,7 @@ Module.register("newsfeed", {
 	 * Registers the feeds to be used by the backend.
 	 */
 	registerFeeds () {
-		for (let feed of this.config.feeds) {
+		for (const feed of this.config.feeds) {
 			this.sendSocketNotification("ADD_FEED", {
 				feed: feed,
 				config: this.config
@@ -239,10 +239,10 @@ Module.register("newsfeed", {
 	 */
 	generateFeed (feeds) {
 		let newsItems = [];
-		for (let feed in feeds) {
+		for (const feed in feeds) {
 			const feedItems = feeds[feed];
 			if (this.subscribedToFeed(feed)) {
-				for (let item of feedItems) {
+				for (const item of feedItems) {
 					item.sourceTitle = this.titleForFeed(feed);
 					if (!(this.getFeedProperty(feed, "ignoreOldItems") && Date.now() - new Date(item.pubdate) > this.getFeedProperty(feed, "ignoreOlderThan"))) {
 						newsItems.push(item);
@@ -262,7 +262,7 @@ Module.register("newsfeed", {
 
 		if (this.config.prohibitedWords.length > 0) {
 			newsItems = newsItems.filter(function (item) {
-				for (let word of this.config.prohibitedWords) {
+				for (const word of this.config.prohibitedWords) {
 					if (item.title.toLowerCase().indexOf(word.toLowerCase()) > -1) {
 						return false;
 					}
@@ -273,7 +273,7 @@ Module.register("newsfeed", {
 		newsItems.forEach((item) => {
 			//Remove selected tags from the beginning of rss feed items (title or description)
 			if (this.config.removeStartTags === "title" || this.config.removeStartTags === "both") {
-				for (let startTag of this.config.startTags) {
+				for (const startTag of this.config.startTags) {
 					if (item.title.slice(0, startTag.length) === startTag) {
 						item.title = item.title.slice(startTag.length, item.title.length);
 					}
@@ -282,7 +282,7 @@ Module.register("newsfeed", {
 
 			if (this.config.removeStartTags === "description" || this.config.removeStartTags === "both") {
 				if (this.isShowingDescription) {
-					for (let startTag of this.config.startTags) {
+					for (const startTag of this.config.startTags) {
 						if (item.description.slice(0, startTag.length) === startTag) {
 							item.description = item.description.slice(startTag.length, item.description.length);
 						}
@@ -292,14 +292,14 @@ Module.register("newsfeed", {
 
 			//Remove selected tags from the end of rss feed items (title or description)
 			if (this.config.removeEndTags) {
-				for (let endTag of this.config.endTags) {
+				for (const endTag of this.config.endTags) {
 					if (item.title.slice(-endTag.length) === endTag) {
 						item.title = item.title.slice(0, -endTag.length);
 					}
 				}
 
 				if (this.isShowingDescription) {
-					for (let endTag of this.config.endTags) {
+					for (const endTag of this.config.endTags) {
 						if (item.description.slice(-endTag.length) === endTag) {
 							item.description = item.description.slice(0, -endTag.length);
 						}
@@ -331,7 +331,7 @@ Module.register("newsfeed", {
 	 * @returns {boolean} True if it is subscribed, false otherwise
 	 */
 	subscribedToFeed (feedUrl) {
-		for (let feed of this.config.feeds) {
+		for (const feed of this.config.feeds) {
 			if (feed.url === feedUrl) {
 				return true;
 			}
@@ -345,7 +345,7 @@ Module.register("newsfeed", {
 	 * @returns {string} The title of the feed
 	 */
 	titleForFeed (feedUrl) {
-		for (let feed of this.config.feeds) {
+		for (const feed of this.config.feeds) {
 			if (feed.url === feedUrl) {
 				return feed.title || "";
 			}

defaultmodules/updatenotification/git_helper.js

@@ -76,7 +76,7 @@ class GitHelper {
 	}
 
 	async getStatusInfo (repo) {
-		let gitInfo = {
+		const gitInfo = {
 			module: repo.module,
 			behind: 0, // commits behind
 			current: "", // branch name

defaultmodules/updatenotification/update_helper.js

@@ -77,7 +77,7 @@ class Updater {
 		});
 
 		await Promise.all(parser);
-		let updater = Object.values(this.moduleList);
+		const updater = Object.values(this.moduleList);
 		Log.debug("Update Result:", updater);
 		return updater;
 	}
@@ -92,7 +92,7 @@ class Updater {
 	 * };
 	 */
 	updateProcess (module) {
-		let Result = {
+		const Result = {
 			error: false,
 			updated: false,
 			needRestart: false

defaultmodules/weather/providers/envcanada.js

@@ -252,7 +252,7 @@ class EnvCanadaProvider {
 		// Check if first forecast is Today or Tonight
 		const isToday = forecasts[0].includes("textForecastName=\"Today\"");
 
-		let nextDay = isToday ? 2 : 1;
+		const nextDay = isToday ? 2 : 1;
 		const lastDay = isToday ? 12 : 11;
 
 		// Process first day

defaultmodules/weather/weather.js

@@ -144,7 +144,7 @@ Module.register("weather", {
 			const senderClasses = sender.data.classes.toLowerCase().split(" ");
 			if (senderClasses.indexOf(this.config.calendarClass.toLowerCase()) !== -1) {
 				this.firstEvent = null;
-				for (let event of payload) {
+				for (const event of payload) {
 					if (event.location || event.geo) {
 						this.firstEvent = event;
 						Log.debug("[weather] First upcoming event with location: ", event);