Refactor to ES6

Author: SpaceK33z

.eslintrc

@@ -22,8 +22,7 @@
 		"no-process-exit": "warn",
 		"space-in-parens": "error",
 		"no-trailing-spaces": "error",
-		"no-use-before-define": "off",
-		"no-unused-vars": "off",
+		"no-unused-vars": "error",
 		"key-spacing": "error",
 		"space-infix-ops": "error",
 		"no-unsafe-negation": "error",
@@ -44,6 +43,8 @@
 			}
 		}],
 		"no-console": "off",
-		"valid-jsdoc": "error"
+		"valid-jsdoc": "error",
+		"no-useless-computed-key": "error",
+		"prefer-const": "error"
 	}
 }

bin/webpack-dev-server.js

@@ -1,63 +1,64 @@
 #!/usr/bin/env node
+"use strict";
 
-var path = require("path");
-var open = require("opn");
-var fs = require("fs");
-var net = require("net");
-var url = require("url");
-var portfinder = require("portfinder");
+const path = require("path");
+const open = require("opn");
+const fs = require("fs");
+const net = require("net");
+const url = require("url");
+const portfinder = require("portfinder");
 
 // Local version replaces global one
 try {
-	var localWebpackDevServer = require.resolve(path.join(process.cwd(), "node_modules", "webpack-dev-server", "bin", "webpack-dev-server.js"));
+	const localWebpackDevServer = require.resolve(path.join(process.cwd(), "node_modules", "webpack-dev-server", "bin", "webpack-dev-server.js"));
 	if(__filename !== localWebpackDevServer) {
 		return require(localWebpackDevServer);
 	}
 } catch(e) {}
 
-var Server = require("../lib/Server");
-var webpack = require("webpack");
+const Server = require("../lib/Server");
+const webpack = require("webpack");
 
 function versionInfo() {
-	return "webpack-dev-server " + require("../package.json").version + "\n" +
-		"webpack " + require("webpack/package.json").version;
+	return `webpack-dev-server ${require("../package.json").version}\n` +
+		`webpack ${require("webpack/package.json").version}`;
 }
 
 function colorInfo(useColor, msg) {
 	if(useColor)
 		// Make text blue and bold, so it *pops*
-		return "\u001b[1m\u001b[34m" + msg + "\u001b[39m\u001b[22m";
+		return `\u001b[1m\u001b[34m${msg}\u001b[39m\u001b[22m`;
 	return msg;
 }
 
 function colorError(useColor, msg) {
 	if(useColor)
 		// Make text red and bold, so it *pops*
-		return "\u001b[1m\u001b[31m" + msg + "\u001b[39m\u001b[22m";
+		return `\u001b[1m\u001b[31m${msg}\u001b[39m\u001b[22m`;
 	return msg;
 }
 
-var yargs = require("yargs")
-	.usage(versionInfo() +
-		"\nUsage: http://webpack.github.io/docs/webpack-dev-server.html");
+const yargs = require("yargs")
+	.usage(`${versionInfo()
+		}\nUsage: http://webpack.github.io/docs/webpack-dev-server.html`);
 
 require("webpack/bin/config-yargs")(yargs);
 
 // It is important that this is done after the webpack yargs config,
 // so it overrides webpack's version info.
 yargs.version(versionInfo);
 
-var ADVANCED_GROUP = "Advanced options:";
-var DISPLAY_GROUP = "Stats options:";
-var SSL_GROUP = "SSL options:";
-var CONNECTION_GROUP = "Connection options:";
-var RESPONSE_GROUP = "Response options:";
-var BASIC_GROUP = "Basic options:";
+const ADVANCED_GROUP = "Advanced options:";
+const DISPLAY_GROUP = "Stats options:";
+const SSL_GROUP = "SSL options:";
+const CONNECTION_GROUP = "Connection options:";
+const RESPONSE_GROUP = "Response options:";
+const BASIC_GROUP = "Basic options:";
 
 // Taken out of yargs because we must know if
 // it wasn't given by the user, in which case
 // we should use portfinder.
-var DEFAULT_PORT = 8080;
+const DEFAULT_PORT = 8080;
 
 yargs.options({
 	"lazy": {
@@ -185,9 +186,9 @@ yargs.options({
 	}
 });
 
-var argv = yargs.argv;
+const argv = yargs.argv;
 
-var wpOpt = require("webpack/bin/convert-argv")(yargs, argv, {
+const wpOpt = require("webpack/bin/convert-argv")(yargs, argv, {
 	outputFilename: "/bundle.js"
 });
 
@@ -201,9 +202,9 @@ function processOptions(wpOpt) {
 		return;
 	}
 
-	var firstWpOpt = Array.isArray(wpOpt) ? wpOpt[0] : wpOpt;
+	const firstWpOpt = Array.isArray(wpOpt) ? wpOpt[0] : wpOpt;
 
-	var options = wpOpt.devServer || firstWpOpt.devServer || {};
+	const options = wpOpt.devServer || firstWpOpt.devServer || {};
 
 	if(argv.host !== "localhost" || !options.host)
 		options.host = argv.host;
@@ -217,7 +218,7 @@ function processOptions(wpOpt) {
 	if(!options.publicPath) {
 		options.publicPath = firstWpOpt.output && firstWpOpt.output.publicPath || "";
 		if(!/^(https?:)?\/\//.test(options.publicPath) && options.publicPath[0] !== "/")
-			options.publicPath = "/" + options.publicPath;
+			options.publicPath = `/${options.publicPath}`;
 	}
 
 	if(!options.filename)
@@ -326,17 +327,17 @@ function processOptions(wpOpt) {
 }
 
 function startDevServer(wpOpt, options) {
-	var protocol = options.https ? "https" : "http";
+	const protocol = options.https ? "https" : "http";
 
 	// the formatted domain (url without path) of the webpack server
-	var domain = url.format({
+	const domain = url.format({
 		protocol: protocol,
 		hostname: options.host,
 		port: options.socket ? 0 : options.port.toString()
 	});
 
 	if(options.inline !== false) {
-		var devClient = [require.resolve("../client/") + "?" + (options.public ? protocol + "://" + options.public : domain)];
+		const devClient = [`${require.resolve("../client/")}?${options.public ? `${protocol}://${options.public}` : domain}`];
 
 		if(options.hotOnly)
 			devClient.push("webpack/hot/only-dev-server");
@@ -354,7 +355,7 @@ function startDevServer(wpOpt, options) {
 		});
 	}
 
-	var compiler;
+	let compiler;
 	try {
 		compiler = webpack(wpOpt);
 	} catch(e) {
@@ -371,13 +372,13 @@ function startDevServer(wpOpt, options) {
 		}));
 	}
 
-	var uri = domain + (options.inline !== false || options.lazy === true ? "/" : "/webpack-dev-server/");
+	const uri = domain + (options.inline !== false || options.lazy === true ? "/" : "/webpack-dev-server/");
 
-	var server;
+	let server;
 	try {
 		server = new Server(compiler, options);
 	} catch(e) {
-		var OptionsValidationError = require("../lib/OptionsValidationError");
+		const OptionsValidationError = require("../lib/OptionsValidationError");
 		if(e instanceof OptionsValidationError) {
 			console.error(colorError(options.stats.colors, e.message));
 			process.exit(1); // eslint-disable-line
@@ -388,7 +389,7 @@ function startDevServer(wpOpt, options) {
 	if(options.socket) {
 		server.listeningApp.on("error", function(e) {
 			if(e.code === "EADDRINUSE") {
-				var clientSocket = new net.Socket();
+				const clientSocket = new net.Socket();
 				clientSocket.on("error", function(e) {
 					if(e.code === "ECONNREFUSED") {
 						// No other server listening on this socket so it can be safely removed
@@ -405,7 +406,7 @@ function startDevServer(wpOpt, options) {
 		});
 		server.listen(options.socket, options.host, function(err) {
 			if(err) throw err;
-			var READ_WRITE = 438; // chmod 666 (rw rw rw)
+			const READ_WRITE = 438; // chmod 666 (rw rw rw)
 			fs.chmod(options.socket, READ_WRITE, function(err) {
 				if(err) throw err;
 				reportReadiness(uri, options);
@@ -420,19 +421,19 @@ function startDevServer(wpOpt, options) {
 }
 
 function reportReadiness(uri, options) {
-	var useColor = argv.color;
-	var startSentence = "Project is running at " + colorInfo(useColor, uri)
+	const useColor = argv.color;
+	let startSentence = `Project is running at ${colorInfo(useColor, uri)}`
 	if(options.socket) {
-		startSentence = "Listening to socket at " + colorInfo(useColor, options.socket);
+		startSentence = `Listening to socket at ${colorInfo(useColor, options.socket)}`;
 	}
 	console.log((argv["progress"] ? "\n" : "") + startSentence);
 
-	console.log("webpack output is served from " + colorInfo(useColor, options.publicPath));
-	var contentBase = Array.isArray(options.contentBase) ? options.contentBase.join(", ") : options.contentBase;
+	console.log(`webpack output is served from ${colorInfo(useColor, options.publicPath)}`);
+	const contentBase = Array.isArray(options.contentBase) ? options.contentBase.join(", ") : options.contentBase;
 	if(contentBase)
-		console.log("Content not from webpack is served from " + colorInfo(useColor, contentBase));
+		console.log(`Content not from webpack is served from ${colorInfo(useColor, contentBase)}`);
 	if(options.historyApiFallback)
-		console.log("404s will fallback to " + colorInfo(useColor, options.historyApiFallback.index || "/index.html"));
+		console.log(`404s will fallback to ${colorInfo(useColor, options.historyApiFallback.index || "/index.html")}`);
 	if(options.open)
 		open(uri);
 }

examples/hmr/webpack.config.js

@@ -1,4 +1,6 @@
-var webpack = require("webpack");
+"use strict";
+
+const webpack = require("webpack");
 
 module.exports = {
 	context: __dirname,

examples/listen-socket/check-socket.js

@@ -1,8 +1,8 @@
 "use strict";
 
-var net = require("net");
+const net = require("net");
 
-var client = net.createConnection("./webpack.sock");
+const client = net.createConnection("./webpack.sock");
 client.on("connect", function() {
 	console.log("Successfully connected to socket, exiting");
 	process.exit(1); // eslint-disable-line

examples/node-api-middleware/server.js

@@ -1,15 +1,17 @@
-var Webpack = require("webpack");
-var WebpackDevServer = require("../../lib/Server");
-var webpackConfig = require("./webpack.config");
+"use strict";
 
-var compiler = Webpack(webpackConfig);
-var server = new WebpackDevServer(compiler, {
+const Webpack = require("webpack");
+const WebpackDevServer = require("../../lib/Server");
+const webpackConfig = require("./webpack.config");
+
+const compiler = Webpack(webpackConfig);
+const server = new WebpackDevServer(compiler, {
 	stats: {
 		colors: true
 	},
 	setup: function(app) {
 		app.use(function(req, res, next) {
-			console.log("Using middleware for " + req.url);
+			console.log(`Using middleware for ${req.url}`);
 			next();
 		});
 	}

examples/node-api-simple/server.js

@@ -1,9 +1,11 @@
-var Webpack = require("webpack");
-var WebpackDevServer = require("../../lib/Server");
-var webpackConfig = require("./webpack.config");
+"use strict";
 
-var compiler = Webpack(webpackConfig);
-var server = new WebpackDevServer(compiler, {
+const Webpack = require("webpack");
+const WebpackDevServer = require("../../lib/Server");
+const webpackConfig = require("./webpack.config");
+
+const compiler = Webpack(webpackConfig);
+const server = new WebpackDevServer(compiler, {
 	stats: {
 		colors: true
 	}

examples/proxy-hot-reload/webpack.config.js

@@ -1,7 +1,9 @@
-var fs = require("fs");
+"use strict";
 
-var proxyConfig = require("./proxy-config");
-var proxyOptions = {
+const fs = require("fs");
+
+const proxyConfig = require("./proxy-config");
+let proxyOptions = {
 	context: "/api",
 	target: proxyConfig.target,
 	pathRewrite: proxyConfig.pathRewrite,
@@ -11,7 +13,7 @@ var proxyOptions = {
 fs.watch("./proxy-config.js", function() {
 	delete require.cache[require.resolve("./proxy-config")];
 	try {
-		var newProxyConfig = require("./proxy-config");
+		const newProxyConfig = require("./proxy-config");
 		if(proxyOptions.target !== newProxyConfig.target) {
 			console.log("Proxy target changed:", newProxyConfig.target);
 			proxyOptions = {

examples/webpack-config-array/webpack.config.js

@@ -1,4 +1,6 @@
-var webpack = require("webpack");
+"use strict";
+
+const webpack = require("webpack");
 module.exports = [
 	{
 		context: __dirname,

lib/OptionsValidationError.js

@@ -1,14 +1,16 @@
-var optionsSchema = require("./optionsSchema.json");
+"use strict";
+
+const optionsSchema = require("./optionsSchema.json");
 
 function OptionsValidationError(validationErrors) {
 	Error.call(this);
 	Error.captureStackTrace(this, OptionsValidationError);
 	this.name = "WebpackDevServerOptionsValidationError";
-	this.message = "Invalid configuration object. " +
-		"webpack-dev-server has been initialised using a configuration object that does not match the API schema.\n" +
+	this.message = `${"Invalid configuration object. " +
+		"webpack-dev-server has been initialised using a configuration object that does not match the API schema.\n"}${
 		validationErrors.map(function(err) {
-			return " - " + indent(OptionsValidationError.formatValidationError(err), "   ", false);
-		}).join("\n");
+			return ` - ${indent(OptionsValidationError.formatValidationError(err), "   ", false)}`;
+		}).join("\n")}`;
 	this.validationErrors = validationErrors;
 }
 module.exports = OptionsValidationError;
@@ -17,48 +19,48 @@ OptionsValidationError.prototype = Object.create(Error.prototype);
 OptionsValidationError.prototype.constructor = OptionsValidationError;
 
 OptionsValidationError.formatValidationError = function formatValidationError(err) {
-	var dataPath = "configuration" + err.dataPath;
+	const dataPath = `configuration${err.dataPath}`;
 	switch(err.keyword) {
 		case "additionalProperties":
-			return dataPath + " has an unknown property '" + err.params.additionalProperty + "'. These properties are valid:\n" +
-				getSchemaPartText(err.parentSchema);
+			return `${dataPath} has an unknown property '${err.params.additionalProperty}'. These properties are valid:\n${
+				getSchemaPartText(err.parentSchema)}`;
 		case "oneOf":
 		case "anyOf":
 		case "enum":
-			return dataPath + " should be one of these:\n" +
-				getSchemaPartText(err.parentSchema);
+			return `${dataPath} should be one of these:\n${
+				getSchemaPartText(err.parentSchema)}`;
 		case "allOf":
-			return dataPath + " should be:\n" +
-				getSchemaPartText(err.parentSchema);
+			return `${dataPath} should be:\n${
+				getSchemaPartText(err.parentSchema)}`;
 		case "type":
 			switch(err.params.type) {
 				case "object":
-					return dataPath + " should be an object.";
+					return `${dataPath} should be an object.`;
 				case "array":
-					return dataPath + " should be an array.";
+					return `${dataPath} should be an array.`;
 				case "string":
-					return dataPath + " should be a string.";
+					return `${dataPath} should be a string.`;
 				case "boolean":
-					return dataPath + " should be a boolean.";
+					return `${dataPath} should be a boolean.`;
 				case "number":
-					return dataPath + " should be a number.";
+					return `${dataPath} should be a number.`;
 			}
-			return dataPath + " should be " + err.params.type + ":\n" +
-				getSchemaPartText(err.parentSchema);
+			return `${dataPath} should be ${err.params.type}:\n${
+				getSchemaPartText(err.parentSchema)}`;
 		case "instanceof":
-			return dataPath + " should be an instance of " + getSchemaPartText(err.parentSchema) + ".";
-		case "required":
-			var missingProperty = err.params.missingProperty.replace(/^\./, "");
-			return dataPath + " misses the property '" + missingProperty + "'.\n" +
-				getSchemaPartText(err.parentSchema, ["properties", missingProperty]);
+			return `${dataPath} should be an instance of ${getSchemaPartText(err.parentSchema)}.`;
+		case "required": // eslint-disable-line no-case-declarations
+			const missingProperty = err.params.missingProperty.replace(/^\./, "");
+			return `${dataPath} misses the property '${missingProperty}'.\n${
+				getSchemaPartText(err.parentSchema, ["properties", missingProperty])}`;
 		case "minLength":
 			if(err.params.limit === 1)
-				return dataPath + " should not be empty.";
+				return `${dataPath} should not be empty.`;
 			else
-				return dataPath + " " + err.message;
+				return `${dataPath} ${err.message}`;
 		default:
-			return dataPath + " " + err.message + " (" + JSON.stringify(err, 0, 2) + ").\n" +
-				getSchemaPartText(err.parentSchema);
+			return `${dataPath} ${err.message} (${JSON.stringify(err, 0, 2)}).\n${
+				getSchemaPartText(err.parentSchema)}`;
 	}
 }
 
@@ -70,9 +72,9 @@ function getSchemaPart(path, parents, additionalPath) {
 		additionalPath = additionalPath.split("/");
 		path = path.concat(additionalPath);
 	}
-	var schemaPart = optionsSchema;
-	for(var i = 1; i < path.length; i++) {
-		var inner = schemaPart[path[i]];
+	let schemaPart = optionsSchema;
+	for(let i = 1; i < path.length; i++) {
+		const inner = schemaPart[path[i]];
 		if(inner)
 			schemaPart = inner;
 	}
@@ -81,16 +83,16 @@ function getSchemaPart(path, parents, additionalPath) {
 
 function getSchemaPartText(schemaPart, additionalPath) {
 	if(additionalPath) {
-		for(var i = 0; i < additionalPath.length; i++) {
-			var inner = schemaPart[additionalPath[i]];
+		for(let i = 0; i < additionalPath.length; i++) {
+			const inner = schemaPart[additionalPath[i]];
 			if(inner)
 				schemaPart = inner;
 		}
 	}
 	while(schemaPart.$ref) schemaPart = getSchemaPart(schemaPart.$ref);
-	var schemaText = OptionsValidationError.formatSchema(schemaPart);
+	let schemaText = OptionsValidationError.formatSchema(schemaPart);
 	if(schemaPart.description)
-		schemaText += "\n" + schemaPart.description;
+		schemaText += `\n${schemaPart.description}`;
 	return schemaText;
 }
 
@@ -111,18 +113,18 @@ function formatSchema(schema, prevSchemas) {
 			return "number";
 		case "object":
 			if(schema.properties) {
-				var required = schema.required || [];
-				return "object { " + Object.keys(schema.properties).map(function(property) {
-					if(required.indexOf(property) < 0) return property + "?";
+				const required = schema.required || [];
+				return `object { ${Object.keys(schema.properties).map(function(property) {
+					if(required.indexOf(property) < 0) return `${property}?`;
 					return property;
-				}).concat(schema.additionalProperties ? ["..."] : []).join(", ") + " }";
+				}).concat(schema.additionalProperties ? ["..."] : []).join(", ")} }`;
 			}
 			if(schema.additionalProperties) {
-				return "object { <key>: " + formatInnerSchema(schema.additionalProperties) + " }";
+				return `object { <key>: ${formatInnerSchema(schema.additionalProperties)} }`;
 			}
 			return "object";
 		case "array":
-			return "[" + formatInnerSchema(schema.items) + "]";
+			return `[${formatInnerSchema(schema.items)}]`;
 	}
 	switch(schema.instanceof) {
 		case "Function":
@@ -142,9 +144,9 @@ function formatSchema(schema, prevSchemas) {
 
 function indent(str, prefix, firstLine) {
 	if(firstLine) {
-		return prefix + str.replace(/\n(?!$)/g, "\n" + prefix);
+		return prefix + str.replace(/\n(?!$)/g, `\n${prefix}`);
 	} else {
-		return str.replace(/\n(?!$)/g, "\n" + prefix);
+		return str.replace(/\n(?!$)/g, `\n${prefix}`);
 	}
 }
 

lib/Server.js

@@ -1,26 +1,28 @@
-var fs = require("fs");
-var chokidar = require("chokidar");
-var path = require("path");
-var webpackDevMiddleware = require("webpack-dev-middleware");
-var express = require("express");
-var compress = require("compression");
-var sockjs = require("sockjs");
-var http = require("http");
-var spdy = require("spdy");
-var httpProxyMiddleware = require("http-proxy-middleware");
-var serveIndex = require("serve-index");
-var historyApiFallback = require("connect-history-api-fallback");
-var webpack = require("webpack");
-var OptionsValidationError = require("./OptionsValidationError");
-var optionsSchema = require("./optionsSchema.json");
-
-var clientStats = { errorDetails: false };
+"use strict";
+
+const fs = require("fs");
+const chokidar = require("chokidar");
+const path = require("path");
+const webpackDevMiddleware = require("webpack-dev-middleware");
+const express = require("express");
+const compress = require("compression");
+const sockjs = require("sockjs");
+const http = require("http");
+const spdy = require("spdy");
+const httpProxyMiddleware = require("http-proxy-middleware");
+const serveIndex = require("serve-index");
+const historyApiFallback = require("connect-history-api-fallback");
+const webpack = require("webpack");
+const OptionsValidationError = require("./OptionsValidationError");
+const optionsSchema = require("./optionsSchema.json");
+
+const clientStats = { errorDetails: false };
 
 function Server(compiler, options) {
 	// Default options
 	if(!options) options = {};
 
-	var validationErrors = webpack.validateSchema(optionsSchema, options);
+	const validationErrors = webpack.validateSchema(optionsSchema, options);
 	if(validationErrors.length) {
 		throw new OptionsValidationError(validationErrors);
 	}
@@ -36,7 +38,7 @@ function Server(compiler, options) {
 	this.contentBaseWatchers = [];
 
 	// Listening for events
-	var invalidPlugin = function() {
+	const invalidPlugin = function() {
 		this.sockWrite(this.sockets, "invalid");
 	}.bind(this);
 	compiler.plugin("compile", invalidPlugin);
@@ -47,7 +49,7 @@ function Server(compiler, options) {
 	}.bind(this));
 
 	// Init express server
-	var app = this.app = new express();
+	const app = this.app = new express();
 
 	// middleware for serving webpack bundle
 	this.middleware = webpackDevMiddleware(compiler, options);
@@ -76,22 +78,22 @@ function Server(compiler, options) {
 		res.setHeader("Content-Type", "text/html");
 		/* eslint-disable quotes */
 		res.write('<!DOCTYPE html><html><head><meta charset="utf-8"/></head><body>');
-		var path = this.middleware.getFilenameFromUrl(options.publicPath || "/");
-		var fs = this.middleware.fileSystem;
+		const path = this.middleware.getFilenameFromUrl(options.publicPath || "/");
+		const fs = this.middleware.fileSystem;
 
 		function writeDirectory(baseUrl, basePath) {
-			var content = fs.readdirSync(basePath);
+			const content = fs.readdirSync(basePath);
 			res.write("<ul>");
 			content.forEach(function(item) {
-				var p = basePath + "/" + item;
+				const p = `${basePath}/${item}`;
 				if(fs.statSync(p).isFile()) {
 					res.write('<li><a href="');
 					res.write(baseUrl + item);
 					res.write('">');
 					res.write(item);
 					res.write('</a></li>');
 					if(/\.js$/.test(item)) {
-						var htmlItem = item.substr(0, item.length - 3);
+						const htmlItem = item.substr(0, item.length - 3);
 						res.write('<li><a href="');
 						res.write(baseUrl + htmlItem);
 						res.write('">');
@@ -106,7 +108,7 @@ function Server(compiler, options) {
 					res.write('<li>');
 					res.write(item);
 					res.write('<br>');
-					writeDirectory(baseUrl + item + "/", p);
+					writeDirectory(`${baseUrl + item}/`, p);
 					res.write('</li>');
 				}
 			});
@@ -117,14 +119,14 @@ function Server(compiler, options) {
 		res.end("</body></html>");
 	}.bind(this));
 
-	var contentBase;
+	let contentBase;
 	if(options.contentBase !== undefined) {
 		contentBase = options.contentBase;
 	} else {
 		contentBase = process.cwd();
 	}
 
-	var features = {
+	const features = {
 		compress: function() {
 			if(options.compress) {
 				// Enable gzip compression.
@@ -146,9 +148,9 @@ function Server(compiler, options) {
 				 */
 				if(!Array.isArray(options.proxy)) {
 					options.proxy = Object.keys(options.proxy).map(function(context) {
-						var proxyOptions;
+						let proxyOptions;
 						// For backwards compatibility reasons.
-						var correctedContext = context.replace(/^\*$/, "**").replace(/\/\*$/, "");
+						const correctedContext = context.replace(/^\*$/, "**").replace(/\/\*$/, "");
 
 						if(typeof options.proxy[context] === "string") {
 							proxyOptions = {
@@ -165,8 +167,8 @@ function Server(compiler, options) {
 					});
 				}
 
-				var getProxyMiddleware = function(proxyConfig) {
-					var context = proxyConfig.context || proxyConfig.path;
+				const getProxyMiddleware = function(proxyConfig) {
+					const context = proxyConfig.context || proxyConfig.path;
 
 					// It is possible to use the `bypass` method without a `target`.
 					// However, the proxy middleware has no use in this case, and will fail to instantiate.
@@ -192,8 +194,8 @@ function Server(compiler, options) {
 				 * ]
 				 */
 				options.proxy.forEach(function(proxyConfigOrCallback) {
-					var proxyConfig;
-					var proxyMiddleware;
+					let proxyConfig;
+					let proxyMiddleware;
 
 					if(typeof proxyConfigOrCallback === "function") {
 						proxyConfig = proxyConfigOrCallback();
@@ -205,14 +207,14 @@ function Server(compiler, options) {
 
 					app.use(function(req, res, next) {
 						if(typeof proxyConfigOrCallback === "function") {
-							var newProxyConfig = proxyConfigOrCallback();
+							const newProxyConfig = proxyConfigOrCallback();
 							if(newProxyConfig !== proxyConfig) {
 								proxyConfig = newProxyConfig;
 								proxyMiddleware = getProxyMiddleware(proxyConfig);
 							}
 						}
-						var bypass = typeof proxyConfig.bypass === "function";
-						var bypassUrl = bypass && proxyConfig.bypass(req, res, proxyConfig) || false;
+						const bypass = typeof proxyConfig.bypass === "function";
+						const bypassUrl = bypass && proxyConfig.bypass(req, res, proxyConfig) || false;
 
 						if(bypassUrl) {
 							req.url = bypassUrl;
@@ -257,7 +259,7 @@ function Server(compiler, options) {
 				// Redirect every request to the port contentBase
 				app.get("*", function(req, res) {
 					res.writeHead(302, {
-						"Location": "//localhost:" + contentBase + req.path + (req._parsedUrl.search || "")
+						"Location": `//localhost:${contentBase}${req.path}${req._parsedUrl.search || ""}`
 					});
 					res.end();
 				});
@@ -308,7 +310,7 @@ function Server(compiler, options) {
 		}.bind(this)
 	};
 
-	var defaultFeatures = ["setup", "headers", "middleware"];
+	const defaultFeatures = ["setup", "headers", "middleware"];
 	if(options.proxy)
 		defaultFeatures.push("proxy", "middleware");
 	if(contentBase !== false)
@@ -341,7 +343,7 @@ function Server(compiler, options) {
 		}
 
 		// Use built-in self-signed certificate if no certificate was configured
-		var fakeCert = fs.readFileSync(path.join(__dirname, "../ssl/server.pem"));
+		const fakeCert = fs.readFileSync(path.join(__dirname, "../ssl/server.pem"));
 		options.https.key = options.https.key || fakeCert;
 		options.https.cert = options.https.cert || fakeCert;
 
@@ -363,7 +365,7 @@ Server.prototype.use = function() {
 
 Server.prototype.setContentHeaders = function(req, res, next) {
 	if(this.headers) {
-		for(var name in this.headers) {
+		for(const name in this.headers) {
 			res.setHeader(name, this.headers[name]);
 		}
 	}
@@ -373,8 +375,8 @@ Server.prototype.setContentHeaders = function(req, res, next) {
 
 // delegate listen call and init sockjs
 Server.prototype.listen = function() {
-	var returnValue = this.listeningApp.listen.apply(this.listeningApp, arguments);
-	var sockServer = sockjs.createServer({
+	const returnValue = this.listeningApp.listen.apply(this.listeningApp, arguments);
+	const sockServer = sockjs.createServer({
 		// Use provided up-to-date sockjs-client
 		sockjs_url: "/__webpack_dev_server__/sockjs.bundle.js",
 		// Limit useless logs
@@ -389,7 +391,7 @@ Server.prototype.listen = function() {
 		this.sockets.push(conn);
 
 		conn.on("close", function() {
-			var connIndex = this.sockets.indexOf(conn);
+			const connIndex = this.sockets.indexOf(conn);
 			if(connIndex >= 0) {
 				this.sockets.splice(connIndex, 1);
 			}
@@ -435,9 +437,9 @@ Server.prototype.sockWrite = function(sockets, type, data) {
 }
 
 Server.prototype.serveMagicHtml = function(req, res, next) {
-	var _path = req.path;
+	const _path = req.path;
 	try {
-		if(!this.middleware.fileSystem.statSync(this.middleware.getFilenameFromUrl(_path + ".js")).isFile())
+		if(!this.middleware.fileSystem.statSync(this.middleware.getFilenameFromUrl(`${_path}.js`)).isFile())
 			return next();
 		// Serve a page that executes the javascript
 		/* eslint-disable quotes */
@@ -473,7 +475,7 @@ Server.prototype._sendStats = function(sockets, stats, force) {
 }
 
 Server.prototype._watch = function(path) {
-	var watcher = chokidar.watch(path).on("change", function() {
+	const watcher = chokidar.watch(path).on("change", function() {
 		this.sockWrite(this.sockets, "content-changed");
 	}.bind(this))
 

test/Compress.test.js

@@ -1,10 +1,12 @@
-var request = require("supertest");
-var helper = require("./helper");
-var config = require("./fixtures/simple-config/webpack.config");
+"use strict";
+
+const request = require("supertest");
+const helper = require("./helper");
+const config = require("./fixtures/simple-config/webpack.config");
 
 describe("Compress", function() {
-	var server;
-	var req;
+	let server;
+	let req;
 
 	before(function(done) {
 		server = helper.start(config, {

test/ContentBase.test.js

@@ -1,15 +1,17 @@
-var request = require("supertest");
-var path = require("path");
-var helper = require("./helper");
-var config = require("./fixtures/contentbase-config/webpack.config");
+"use strict";
+
+const request = require("supertest");
+const path = require("path");
+const helper = require("./helper");
+const config = require("./fixtures/contentbase-config/webpack.config");
 require("mocha-sinon");
 
-var contentBasePublic = path.join(__dirname, "fixtures/contentbase-config/public");
-var contentBaseOther = path.join(__dirname, "fixtures/contentbase-config/other");
+const contentBasePublic = path.join(__dirname, "fixtures/contentbase-config/public");
+const contentBaseOther = path.join(__dirname, "fixtures/contentbase-config/other");
 
 describe("ContentBase", function() {
-	var server;
-	var req;
+	let server;
+	let req;
 	afterEach(helper.close);
 
 	describe("to directory", function() {

test/HistoryApiFallback.test.js

@@ -1,13 +1,15 @@
-var path = require("path");
-var request = require("supertest");
-var helper = require("./helper");
-var config = require("./fixtures/historyapifallback-config/webpack.config");
-var config2 = require("./fixtures/historyapifallback-2-config/webpack.config");
-var config3 = require("./fixtures/historyapifallback-3-config/webpack.config");
+"use strict";
+
+const path = require("path");
+const request = require("supertest");
+const helper = require("./helper");
+const config = require("./fixtures/historyapifallback-config/webpack.config");
+const config2 = require("./fixtures/historyapifallback-2-config/webpack.config");
+const config3 = require("./fixtures/historyapifallback-3-config/webpack.config");
 
 describe("HistoryApiFallback", function() {
-	var server;
-	var req;
+	let server;
+	let req;
 
 	afterEach(helper.close);
 

test/Lazy.test.js

@@ -1,6 +1,8 @@
-var should = require("should");
-var helper = require("./helper");
-var config = require("./fixtures/simple-config/webpack.config");
+"use strict";
+
+const should = require("should");
+const helper = require("./helper");
+const config = require("./fixtures/simple-config/webpack.config");
 
 describe("Lazy", function() {
 	afterEach(helper.close);

test/Routes.test.js

@@ -1,15 +1,17 @@
-var request = require("supertest");
-var fs = require("fs");
-var path = require("path");
-var helper = require("./helper");
-var config = require("./fixtures/simple-config/webpack.config");
+"use strict";
 
-var directoryIndex = fs.readFileSync(path.join(__dirname, "fixtures/directory-index.txt"), "utf-8");
-var magicHtml = fs.readFileSync(path.join(__dirname, "fixtures/magic-html.txt"), "utf-8");
+const request = require("supertest");
+const fs = require("fs");
+const path = require("path");
+const helper = require("./helper");
+const config = require("./fixtures/simple-config/webpack.config");
+
+const directoryIndex = fs.readFileSync(path.join(__dirname, "fixtures/directory-index.txt"), "utf-8");
+const magicHtml = fs.readFileSync(path.join(__dirname, "fixtures/magic-html.txt"), "utf-8");
 
 describe("Routes", function() {
-	var server;
-	var req;
+	let server;
+	let req;
 
 	before(function(done) {
 		server = helper.start(config, {

test/Validation.test.js

@@ -1,14 +1,16 @@
-var config = require("./fixtures/simple-config/webpack.config");
-var OptionsValidationError = require("../lib/OptionsValidationError");
-var Server = require("../lib/Server");
-var webpack = require("webpack");
+"use strict";
+
+const config = require("./fixtures/simple-config/webpack.config");
+const OptionsValidationError = require("../lib/OptionsValidationError");
+const Server = require("../lib/Server");
+const webpack = require("webpack");
 
 describe("Validation", function() {
-	var compiler;
+	let compiler;
 	before(function() {
 		compiler = webpack(config);
 	});
-	var testCases = [{
+	const testCases = [{
 		name: "invalid `hot` configuration",
 		config: { hot: "asdf" },
 		message: [
@@ -42,7 +44,7 @@ describe("Validation", function() {
 		]
 	}];
 	testCases.forEach(function(testCase) {
-		it("should fail validation for " + testCase.name, function() {
+		it(`should fail validation for ${testCase.name}`, function() {
 			try {
 				new Server(compiler, testCase.config);
 			} catch(e) {

test/helper.js

@@ -1,14 +1,16 @@
-var Server = require("../lib/Server");
-var webpack = require("webpack");
+"use strict";
 
-var server;
+const Server = require("../lib/Server");
+const webpack = require("webpack");
+
+let server;
 
 module.exports = {
 	start: function(config, options, done) {
 		if(options.quiet === undefined) {
 			options.quiet = true;
 		}
-		var compiler = webpack(config);
+		const compiler = webpack(config);
 		server = new Server(compiler, options);
 
 		server.listen(8080, "localhost", function(err) {