fix(perf): reduced initial start time (#4818)

Author: alexander-akait

lib/Server.js

@@ -6,8 +6,6 @@ const url = require("url");
 const util = require("util");
 const fs = require("graceful-fs");
 const ipaddr = require("ipaddr.js");
-const defaultGateway = require("default-gateway");
-const express = require("express");
 const { validate } = require("schema-utils");
 const schema = require("./options.json");
 
@@ -210,6 +208,34 @@ if (!process.env.WEBPACK_SERVE) {
   process.env.WEBPACK_SERVE = true;
 }
 
+/**
+ * @template T
+ * @param fn {(function(): any) | undefined}
+ * @returns {function(): T}
+ */
+const memoize = (fn) => {
+  let cache = false;
+  /** @type {T} */
+  let result;
+
+  return () => {
+    if (cache) {
+      return result;
+    }
+
+    result = /** @type {function(): any} */ (fn)();
+    cache = true;
+    // Allow to clean up memory for fn
+    // and all dependent resources
+    // eslint-disable-next-line no-undefined
+    fn = undefined;
+
+    return result;
+  };
+};
+
+const getExpress = memoize(() => require("express"));
+
 class Server {
   /**
    * @param {Configuration | Compiler | MultiCompiler} options
@@ -342,7 +368,7 @@ class Server {
    */
   static async internalIP(family) {
     try {
-      const { gateway } = await defaultGateway[family]();
+      const { gateway } = await require("default-gateway")[family]();
       return Server.findIp(gateway);
     } catch {
       // ignore
@@ -355,7 +381,7 @@ class Server {
    */
   static internalIPSync(family) {
     try {
-      const { gateway } = defaultGateway[family].sync();
+      const { gateway } = require("default-gateway")[family].sync();
       return Server.findIp(gateway);
     } catch {
       // ignore
@@ -1144,7 +1170,7 @@ class Server {
               // Ignore error
             }
 
-            // It is file
+            // It is a file
             return stats ? fs.readFileSync(item) : item;
           }
         };
@@ -1898,8 +1924,7 @@ class Server {
    */
   setupApp() {
     /** @type {import("express").Application | undefined}*/
-    // eslint-disable-next-line new-cap
-    this.app = new /** @type {any} */ (express)();
+    this.app = new /** @type {any} */ (getExpress())();
   }
 
   /**
@@ -2318,7 +2343,7 @@ class Server {
           middlewares.push({
             name: "express-static",
             path: publicPath,
-            middleware: express.static(
+            middleware: getExpress().static(
               staticOption.directory,
               staticOption.staticOptions
             ),
@@ -2373,7 +2398,7 @@ class Server {
             middlewares.push({
               name: "express-static",
               path: publicPath,
-              middleware: express.static(
+              middleware: getExpress().static(
                 staticOption.directory,
                 staticOption.staticOptions
               ),
@@ -3257,7 +3282,7 @@ class Server {
              */
             (error) => {
               if (error.code === "ECONNREFUSED") {
-                // No other server listening on this socket so it can be safely removed
+                // No other server listening on this socket, so it can be safely removed
                 fs.unlinkSync(/** @type {string} */ (this.options.ipc));
 
                 resolve();