perf: decrease initial loading time (#458)

Author: alexander-akait

lib/index.js

@@ -5,9 +5,7 @@
 
 "use strict";
 
-const fs = require("graceful-fs");
-const CachedInputFileSystem = require("./CachedInputFileSystem");
-const ResolverFactory = require("./ResolverFactory");
+const memoize = require("./util/memoize");
 
 /** @typedef {import("./CachedInputFileSystem").BaseFileSystem} BaseFileSystem */
 /** @typedef {import("./PnpPlugin").PnpApiImpl} PnpApi */
@@ -36,17 +34,28 @@ const ResolverFactory = require("./ResolverFactory");
  * }} ResolveFunction
  */
 
-const nodeFileSystem = new CachedInputFileSystem(fs, 4000);
+const getCachedFileSystem = memoize(() => require("./CachedInputFileSystem"));
 
-const nodeContext = {
-	environments: ["node+es3+es5+process+native"],
-};
+const getNodeFileSystem = memoize(() => {
+	const fs = require("graceful-fs");
+
+	const CachedInputFileSystem = getCachedFileSystem();
 
-const asyncResolver = ResolverFactory.createResolver({
-	conditionNames: ["node"],
-	extensions: [".js", ".json", ".node"],
-	fileSystem: nodeFileSystem,
+	return new CachedInputFileSystem(fs, 4000);
 });
+const getNodeContext = memoize(() => ({
+	environments: ["node+es3+es5+process+native"],
+}));
+
+const getResolverFactory = memoize(() => require("./ResolverFactory"));
+
+const getAsyncResolver = memoize(() =>
+	getResolverFactory().createResolver({
+		conditionNames: ["node"],
+		extensions: [".js", ".json", ".node"],
+		fileSystem: getNodeFileSystem(),
+	}),
+);
 
 /**
  * @type {ResolveFunctionAsync}
@@ -65,12 +74,12 @@ const resolve =
 			resolveContext = /** @type {ResolveContext} */ (request);
 			request = path;
 			path = context;
-			context = nodeContext;
+			context = getNodeContext();
 		}
 		if (typeof callback !== "function") {
 			callback = /** @type {ResolveCallback} */ (resolveContext);
 		}
-		asyncResolver.resolve(
+		getAsyncResolver().resolve(
 			context,
 			path,
 			/** @type {string} */ (request),
@@ -79,12 +88,14 @@ const resolve =
 		);
 	};
 
-const syncResolver = ResolverFactory.createResolver({
-	conditionNames: ["node"],
-	extensions: [".js", ".json", ".node"],
-	useSyncFileSystemCalls: true,
-	fileSystem: nodeFileSystem,
-});
+const getSyncResolver = memoize(() =>
+	getResolverFactory().createResolver({
+		conditionNames: ["node"],
+		extensions: [".js", ".json", ".node"],
+		useSyncFileSystemCalls: true,
+		fileSystem: getNodeFileSystem(),
+	}),
+);
 
 /**
  * @type {ResolveFunction}
@@ -100,9 +111,9 @@ const resolveSync =
 		if (typeof context === "string") {
 			request = path;
 			path = context;
-			context = nodeContext;
+			context = getNodeContext();
 		}
-		return syncResolver.resolveSync(
+		return getSyncResolver().resolveSync(
 			context,
 			path,
 			/** @type {string} */ (request),
@@ -116,8 +127,8 @@ const resolveSync =
  * @returns {ResolveFunctionAsync} Resolver function
  */
 function create(options) {
-	const resolver = ResolverFactory.createResolver({
-		fileSystem: nodeFileSystem,
+	const resolver = getResolverFactory().createResolver({
+		fileSystem: getNodeFileSystem(),
 		...options,
 	});
 	/**
@@ -133,7 +144,7 @@ function create(options) {
 			resolveContext = /** @type {ResolveContext} */ (request);
 			request = path;
 			path = context;
-			context = nodeContext;
+			context = getNodeContext();
 		}
 		if (typeof callback !== "function") {
 			callback = /** @type {ResolveCallback} */ (resolveContext);
@@ -153,9 +164,9 @@ function create(options) {
  * @returns {ResolveFunction} Resolver function
  */
 function createSync(options) {
-	const resolver = ResolverFactory.createResolver({
+	const resolver = getResolverFactory().createResolver({
 		useSyncFileSystemCalls: true,
-		fileSystem: nodeFileSystem,
+		fileSystem: getNodeFileSystem(),
 		...options,
 	});
 	/**
@@ -168,7 +179,7 @@ function createSync(options) {
 		if (typeof context === "string") {
 			request = path;
 			path = context;
-			context = nodeContext;
+			context = getNodeContext();
 		}
 		return resolver.resolveSync(context, path, /** @type {string} */ (request));
 	};
@@ -196,8 +207,12 @@ module.exports = mergeExports(resolve, {
 			return createSync;
 		},
 	}),
-	ResolverFactory,
-	CachedInputFileSystem,
+	get ResolverFactory() {
+		return getResolverFactory();
+	},
+	get CachedInputFileSystem() {
+		return getCachedFileSystem();
+	},
 	get CloneBasenamePlugin() {
 		return require("./CloneBasenamePlugin");
 	},

lib/util/memoize.js

@@ -0,0 +1,37 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+/**
+ * @template T
+ * @typedef {() => T} FunctionReturning
+ */
+
+/**
+ * @template T
+ * @param {FunctionReturning<T>} fn memorized function
+ * @returns {FunctionReturning<T>} new function
+ */
+const memoize = (fn) => {
+	let cache = false;
+	/** @type {T | undefined} */
+	let result;
+	return () => {
+		if (cache) {
+			return /** @type {T} */ (result);
+		}
+
+		result = fn();
+		cache = true;
+		// Allow to clean up memory for fn
+		// and all dependent resources
+		/** @type {FunctionReturning<T> | undefined} */
+		(fn) = undefined;
+		return /** @type {T} */ (result);
+	};
+};
+
+module.exports = memoize;