diff --git a/lib/AsyncDependenciesBlock.js b/lib/AsyncDependenciesBlock.js
index e251a7d6e..656b1daef 100644
--- a/lib/AsyncDependenciesBlock.js
+++ b/lib/AsyncDependenciesBlock.js
@@ -14,7 +14,7 @@ const DependenciesBlock = require("./DependenciesBlock");
 /** @typedef {import("./util/createHash").Hash} Hash */
 /** @typedef {TODO} GroupOptions */
 
-module.exports = class AsyncDependenciesBlock extends DependenciesBlock {
+class AsyncDependenciesBlock extends DependenciesBlock {
 	/**
 	 * @param {GroupOptions} groupOptions options for the group
 	 * @param {Module} module the Module object
@@ -36,6 +36,8 @@ module.exports = class AsyncDependenciesBlock extends DependenciesBlock {
 		this.request = request;
 		/** @type {DependenciesBlock} */
 		this.parent = undefined;
+		/** @type {[number, number]} */
+		this.range = undefined;
 	}
 
 	/**
@@ -96,4 +98,6 @@ module.exports = class AsyncDependenciesBlock extends DependenciesBlock {
 	sortItems(sortChunks) {
 		super.sortItems();
 	}
-};
+}
+
+module.exports = AsyncDependenciesBlock;
diff --git a/lib/Chunk.js b/lib/Chunk.js
index efe5429b2..f55c6f8d7 100644
--- a/lib/Chunk.js
+++ b/lib/Chunk.js
@@ -109,9 +109,9 @@ class Chunk {
 	 * @param {string=} name of chunk being created, is optional (for subclasses)
 	 */
 	constructor(name) {
-		/** @type {number | null} */
+		/** @type {number | string | null} */
 		this.id = null;
-		/** @type {number[] | null} */
+		/** @type {(number|string)[] | null} */
 		this.ids = null;
 		/** @type {number} */
 		this.debugId = debugId++;
@@ -227,7 +227,7 @@ class Chunk {
 	}
 
 	/**
-	 * @returns {SortableSet} return the modules SortableSet for this chunk
+	 * @returns {SortableSet<Module>} return the modules SortableSet for this chunk
 	 */
 	get modulesIterable() {
 		return this._modules;
diff --git a/lib/ContextModule.js b/lib/ContextModule.js
index 78b7adb0b..fbb1ea3d0 100644
--- a/lib/ContextModule.js
+++ b/lib/ContextModule.js
@@ -14,6 +14,7 @@ const contextify = require("./util/identifier").contextify;
 /** @typedef {import("webpack-sources").Source} Source */
 /** @typedef {import("./Compilation")} Compilation */
 /** @typedef {import("./DependencyTemplates")} DependencyTemplates */
+/** @typedef {import("./Module").LibIdentOptions} LibIdentOptions */
 /** @typedef {import("./Module").SourceContext} SourceContext */
 /** @typedef {import("./RequestShortener")} RequestShortener */
 /** @typedef {import("./RuntimeTemplate")} RuntimeTemplate */
@@ -183,6 +184,10 @@ class ContextModule extends Module {
 		return identifier;
 	}
 
+	/**
+	 * @param {LibIdentOptions} options options
+	 * @returns {string | null} an identifier for library inclusion
+	 */
 	libIdent(options) {
 		let identifier = contextify(options.context, this.context);
 		if (this.options.mode) {
diff --git a/lib/DelegatedModule.js b/lib/DelegatedModule.js
index 613636ed0..af712e120 100644
--- a/lib/DelegatedModule.js
+++ b/lib/DelegatedModule.js
@@ -14,6 +14,7 @@ const DelegatedSourceDependency = require("./dependencies/DelegatedSourceDepende
 /** @typedef {import("webpack-sources").Source} Source */
 /** @typedef {import("./Compilation")} Compilation */
 /** @typedef {import("./DependencyTemplates")} DependencyTemplates */
+/** @typedef {import("./Module").LibIdentOptions} LibIdentOptions */
 /** @typedef {import("./Module").SourceContext} SourceContext */
 /** @typedef {import("./RequestShortener")} RequestShortener */
 /** @typedef {import("./RuntimeTemplate")} RuntimeTemplate */
@@ -36,6 +37,10 @@ class DelegatedModule extends Module {
 		this.delegatedSourceDependency = undefined;
 	}
 
+	/**
+	 * @param {LibIdentOptions} options options
+	 * @returns {string | null} an identifier for library inclusion
+	 */
 	libIdent(options) {
 		return typeof this.originalRequest === "string"
 			? this.originalRequest
diff --git a/lib/DelegatedModuleFactoryPlugin.js b/lib/DelegatedModuleFactoryPlugin.js
index aee02fb98..898b02e12 100644
--- a/lib/DelegatedModuleFactoryPlugin.js
+++ b/lib/DelegatedModuleFactoryPlugin.js
@@ -74,8 +74,8 @@ class DelegatedModuleFactoryPlugin {
 			normalModuleFactory.hooks.module.tap(
 				"DelegatedModuleFactoryPlugin",
 				module => {
-					if (module.libIdent) {
-						const request = module.libIdent(this.options);
+					const request = module.libIdent(this.options);
+					if (request) {
 						if (request && request in this.options.content) {
 							const resolved = this.options.content[request];
 							return new DelegatedModule(
diff --git a/lib/ExternalModule.js b/lib/ExternalModule.js
index d28eacb6d..3d76013be 100644
--- a/lib/ExternalModule.js
+++ b/lib/ExternalModule.js
@@ -13,6 +13,7 @@ const Template = require("./Template");
 /** @typedef {import("./Chunk")} Chunk */
 /** @typedef {import("./Compilation")} Compilation */
 /** @typedef {import("./DependencyTemplates")} DependencyTemplates */
+/** @typedef {import("./Module").LibIdentOptions} LibIdentOptions */
 /** @typedef {import("./Module").SourceContext} SourceContext */
 /** @typedef {import("./RequestShortener")} RequestShortener */
 /** @typedef {import("./RuntimeTemplate")} RuntimeTemplate */
@@ -102,7 +103,7 @@ class ExternalModule extends Module {
 		super("javascript/dynamic", null);
 
 		// Info from Factory
-		/** @type {string} */
+		/** @type {string | string[] | Record<string, string | string[]>} */
 		this.request = request;
 		/** @type {string} */
 		this.externalType = type;
@@ -113,9 +114,10 @@ class ExternalModule extends Module {
 	}
 
 	/**
-	 * @returns {string} the external module identifier
+	 * @param {LibIdentOptions} options options
+	 * @returns {string | null} an identifier for library inclusion
 	 */
-	libIdent() {
+	libIdent(options) {
 		return this.userRequest;
 	}
 
diff --git a/lib/FlagDependencyUsagePlugin.js b/lib/FlagDependencyUsagePlugin.js
index 3c4e4df7c..18e727f30 100644
--- a/lib/FlagDependencyUsagePlugin.js
+++ b/lib/FlagDependencyUsagePlugin.js
@@ -11,6 +11,12 @@
 
 /** @typedef {false | true | string[]} UsedExports */
 
+/**
+ * @template T
+ * @param {T[]} a array (will be modified)
+ * @param {T[]} b array (will be added to a)
+ * @returns {T[]} a again
+ */
 const addToSet = (a, b) => {
 	for (const item of b) {
 		if (!a.includes(item)) a.push(item);
@@ -34,6 +40,12 @@ class FlagDependencyUsagePlugin {
 			compilation.hooks.optimizeDependencies.tap(
 				"FlagDependencyUsagePlugin",
 				modules => {
+					/**
+					 *
+					 * @param {Module} module module to process
+					 * @param {string[] | boolean} usedExports list of used exports
+					 * @returns {void}
+					 */
 					const processModule = (module, usedExports) => {
 						module.used = true;
 						if (module.usedExports === true) return;
diff --git a/lib/FlagInitialModulesAsUsedPlugin.js b/lib/FlagInitialModulesAsUsedPlugin.js
index 69d1026ff..3c7b89778 100644
--- a/lib/FlagInitialModulesAsUsedPlugin.js
+++ b/lib/FlagInitialModulesAsUsedPlugin.js
@@ -5,11 +5,17 @@
 
 "use strict";
 
+/** @typedef {import("./Compiler")} Compiler */
+
 class FlagInitialModulesAsUsedPlugin {
 	constructor(explanation) {
 		this.explanation = explanation;
 	}
 
+	/**
+	 * @param {Compiler} compiler webpack compiler
+	 * @returns {void}
+	 */
 	apply(compiler) {
 		compiler.hooks.compilation.tap(
 			"FlagInitialModulesAsUsedPlugin",
diff --git a/lib/HashedModuleIdsPlugin.js b/lib/HashedModuleIdsPlugin.js
index c8a60bfcd..643092631 100644
--- a/lib/HashedModuleIdsPlugin.js
+++ b/lib/HashedModuleIdsPlugin.js
@@ -33,17 +33,19 @@ class HashedModuleIdsPlugin {
 				"HashedModuleIdsPlugin",
 				modules => {
 					for (const module of modules) {
-						if (module.id === null && module.libIdent) {
+						if (module.id === null) {
 							const id = module.libIdent({
 								context: this.options.context || compiler.options.context
 							});
-							const hash = createHash(options.hashFunction);
-							hash.update(id);
-							const hashId = hash.digest(options.hashDigest);
-							let len = options.hashDigestLength;
-							while (usedIds.has(hashId.substr(0, len))) len++;
-							module.id = hashId.substr(0, len);
-							usedIds.add(module.id);
+							if (id) {
+								const hash = createHash(options.hashFunction);
+								hash.update(id);
+								const hashId = hash.digest(options.hashDigest);
+								let len = options.hashDigestLength;
+								while (usedIds.has(hashId.substr(0, len))) len++;
+								module.id = hashId.substr(0, len);
+								usedIds.add(module.id);
+							}
 						}
 					}
 				}
diff --git a/lib/HotModuleReplacementPlugin.js b/lib/HotModuleReplacementPlugin.js
index 773b43eff..6a48cd09e 100644
--- a/lib/HotModuleReplacementPlugin.js
+++ b/lib/HotModuleReplacementPlugin.js
@@ -20,6 +20,9 @@ const ConstDependency = require("./dependencies/ConstDependency");
 const ModuleHotAcceptDependency = require("./dependencies/ModuleHotAcceptDependency");
 const ModuleHotDeclineDependency = require("./dependencies/ModuleHotDeclineDependency");
 
+/** @typedef {import("./Compiler")} Compiler */
+/** @typedef {import("./Module")} Module */
+
 const hotInitCode = Template.getFunctionContent(
 	require("./HotModuleReplacement.runtime")
 );
@@ -51,6 +54,10 @@ module.exports = class HotModuleReplacementPlugin {
 		this.requestTimeout = this.options.requestTimeout || 10000;
 	}
 
+	/**
+	 * @param {Compiler} compiler webpack compiler
+	 * @returns {void}
+	 */
 	apply(compiler) {
 		const multiStep = this.multiStep;
 		const fullBuildTimeout = this.fullBuildTimeout;
@@ -259,10 +266,14 @@ module.exports = class HotModuleReplacementPlugin {
 							!records.chunkModuleIds
 						)
 							return;
+						/** @type {Set<Module>} */
+						const updatedModules = new Set();
 						for (const module of compilation.modules) {
 							const identifier = module.identifier();
-							let hash = module.hash;
-							module.hotUpdate = records.moduleHashs[identifier] !== hash;
+							const hash = module.hash;
+							if (records.moduleHashs[identifier] !== hash) {
+								updatedModules.add(module);
+							}
 						}
 						const hotUpdateMainContent = {
 							h: compilation.hash,
@@ -276,7 +287,8 @@ module.exports = class HotModuleReplacementPlugin {
 							if (currentChunk) {
 								const newModules = currentChunk
 									.getModules()
-									.filter(module => module.hotUpdate);
+									.filter(module => updatedModules.has(module));
+								/** @type {Set<number|string>} */
 								const allModules = new Set();
 								for (const module of currentChunk.modulesIterable) {
 									allModules.add(module.id);
diff --git a/lib/LibManifestPlugin.js b/lib/LibManifestPlugin.js
index 5b9f654ce..22eec9c02 100644
--- a/lib/LibManifestPlugin.js
+++ b/lib/LibManifestPlugin.js
@@ -47,19 +47,17 @@ class LibManifestPlugin {
 								) {
 									return;
 								}
-								if (module.libIdent) {
-									const ident = module.libIdent({
-										context: this.options.context || compiler.options.context
-									});
-									if (ident) {
-										return {
-											ident,
-											data: {
-												id: module.id,
-												buildMeta: module.buildMeta
-											}
-										};
-									}
+								const ident = module.libIdent({
+									context: this.options.context || compiler.options.context
+								});
+								if (ident) {
+									return {
+										ident,
+										data: {
+											id: module.id,
+											buildMeta: module.buildMeta
+										}
+									};
 								}
 							})
 								.filter(Boolean)
diff --git a/lib/Module.js b/lib/Module.js
index e3bb20503..73c331ba0 100644
--- a/lib/Module.js
+++ b/lib/Module.js
@@ -28,6 +28,11 @@ const SortableSet = require("./util/SortableSet");
  * @property {string=} type the type of source that should be generated
  */
 
+/**
+ * @typedef {Object} LibIdentOptions
+ * @property {string} context absolute context path to which lib ident is relative to
+ */
+
 const EMPTY_RESOLVE_OPTIONS = {};
 
 let debugId = 1000;
@@ -498,6 +503,14 @@ class Module extends DependenciesBlock {
 		throw new Error("Module.size: Must be overriden");
 	}
 
+	/**
+	 * @param {LibIdentOptions} options options
+	 * @returns {string | null} an identifier for library inclusion
+	 */
+	libIdent(options) {
+		return null;
+	}
+
 	/**
 	 * @returns {string | null} absolute path which should be used for condition matching (usually the resource path)
 	 */
diff --git a/lib/NamedModulesPlugin.js b/lib/NamedModulesPlugin.js
index 417676829..e566e1898 100644
--- a/lib/NamedModulesPlugin.js
+++ b/lib/NamedModulesPlugin.js
@@ -26,8 +26,11 @@ class NamedModulesPlugin {
 				const context = this.options.context || compiler.options.context;
 
 				for (const module of modules) {
-					if (module.id === null && module.libIdent) {
-						module.id = module.libIdent({ context });
+					if (module.id === null) {
+						const id = module.libIdent({ context });
+						if (id) {
+							module.id = id;
+						}
 					}
 
 					if (module.id !== null) {
diff --git a/lib/NormalModule.js b/lib/NormalModule.js
index fbf87e722..27db3695e 100644
--- a/lib/NormalModule.js
+++ b/lib/NormalModule.js
@@ -26,6 +26,7 @@ const contextify = require("./util/identifier").contextify;
 /** @typedef {import("webpack-sources").Source} Source */
 /** @typedef {import("./Compilation")} Compilation */
 /** @typedef {import("./DependencyTemplates")} DependencyTemplates */
+/** @typedef {import("./Module").LibIdentOptions} LibIdentOptions */
 /** @typedef {import("./Module").SourceContext} SourceContext */
 /** @typedef {import("./RequestShortener")} RequestShortener */
 /** @typedef {import("./RuntimeTemplate")} RuntimeTemplate */
@@ -121,6 +122,10 @@ class NormalModule extends Module {
 		return requestShortener.shorten(this.userRequest);
 	}
 
+	/**
+	 * @param {LibIdentOptions} options options
+	 * @returns {string | null} an identifier for library inclusion
+	 */
 	libIdent(options) {
 		return contextify(options.context, this.userRequest);
 	}
diff --git a/lib/UmdMainTemplatePlugin.js b/lib/UmdMainTemplatePlugin.js
index 7d0e91d2f..e1e82c653 100644
--- a/lib/UmdMainTemplatePlugin.js
+++ b/lib/UmdMainTemplatePlugin.js
@@ -6,8 +6,11 @@
 "use strict";
 
 const { ConcatSource, OriginalSource } = require("webpack-sources");
+const ExternalModule = require("./ExternalModule");
 const Template = require("./Template");
 
+/** @typedef {import("webpack-sources").Source} Source */
+/** @typedef {import("./Chunk")} Chunk */
 /** @typedef {import("./Compilation")} Compilation */
 
 /**
@@ -85,14 +88,21 @@ class UmdMainTemplatePlugin {
 	apply(compilation) {
 		const { mainTemplate, chunkTemplate, runtimeTemplate } = compilation;
 
+		/**
+		 * @param {Source} source source
+		 * @param {Chunk} chunk chunk
+		 * @param {string} hash Hash
+		 * @returns {Source} new source
+		 */
 		const onRenderWithEntry = (source, chunk, hash) => {
-			let externals = chunk
+			/** @type {ExternalModule[]} */
+			let externals = /** @type {ExternalModule[]} */ (chunk
 				.getModules()
 				.filter(
 					m =>
-						m.external &&
+						m instanceof ExternalModule &&
 						(m.externalType === "umd" || m.externalType === "umd2")
-				);
+				));
 			const optionalExternals = [];
 			let requiredExternals = [];
 			if (this.optionalAmdExternalAsGlobal) {
diff --git a/lib/dependencies/RequireEnsureDependenciesBlock.js b/lib/dependencies/RequireEnsureDependenciesBlock.js
index 86cc8ee94..d62dd787a 100644
--- a/lib/dependencies/RequireEnsureDependenciesBlock.js
+++ b/lib/dependencies/RequireEnsureDependenciesBlock.js
@@ -20,12 +20,17 @@ module.exports = class RequireEnsureDependenciesBlock extends AsyncDependenciesB
 	) {
 		super(chunkName, module, loc, null);
 		this.expr = expr;
+		/** @type {[number, number] | undefined} */
 		const successBodyRange =
 			successExpression &&
 			successExpression.body &&
 			successExpression.body.range;
 		if (successBodyRange) {
-			this.range = [successBodyRange[0] + 1, successBodyRange[1] - 1];
+			const range = /** @type {[number, number]} */ ([
+				successBodyRange[0] + 1,
+				successBodyRange[1] - 1
+			]);
+			this.range = range;
 		}
 		this.chunkNameRange = chunkNameRange;
 		const dep = new RequireEnsureDependency(this);
diff --git a/lib/node/NodeChunkTemplatePlugin.js b/lib/node/NodeChunkTemplatePlugin.js
index 292182a97..f18203bf1 100644
--- a/lib/node/NodeChunkTemplatePlugin.js
+++ b/lib/node/NodeChunkTemplatePlugin.js
@@ -7,7 +7,13 @@
 
 const { ConcatSource } = require("webpack-sources");
 
+/** @typedef {import("../ChunkTemplate")} ChunkTemplate */
+
 class NodeChunkTemplatePlugin {
+	/**
+	 * @param {ChunkTemplate} chunkTemplate the chunk template
+	 * @returns {void}
+	 */
 	apply(chunkTemplate) {
 		chunkTemplate.hooks.render.tap(
 			"NodeChunkTemplatePlugin",
diff --git a/lib/optimize/ConcatenatedModule.js b/lib/optimize/ConcatenatedModule.js
index 4f9047c15..e28b77afc 100644
--- a/lib/optimize/ConcatenatedModule.js
+++ b/lib/optimize/ConcatenatedModule.js
@@ -27,6 +27,7 @@ const createHash = require("../util/createHash");
 /** @typedef {import("../DependencyTemplate").DependencyTemplateContext} DependencyTemplateContext */
 /** @typedef {import("../DependencyTemplates")} DependencyTemplates */
 /** @typedef {import("../InitFragment")} InitFragment */
+/** @typedef {import("../Module").LibIdentOptions} LibIdentOptions */
 /** @typedef {import("../Module").SourceContext} SourceContext */
 /** @typedef {import("../RequestShortener")} RequestShortener */
 /** @typedef {import("../RuntimeTemplate")} RuntimeTemplate */
@@ -410,6 +411,10 @@ class ConcatenatedModule extends Module {
 		);
 	}
 
+	/**
+	 * @param {LibIdentOptions} options options
+	 * @returns {string | null} an identifier for library inclusion
+	 */
 	libIdent(options) {
 		return this.rootModule.libIdent(options);
 	}
diff --git a/lib/optimize/OccurrenceModuleOrderPlugin.js b/lib/optimize/OccurrenceModuleOrderPlugin.js
index fb6344c5f..a8125c47e 100644
--- a/lib/optimize/OccurrenceModuleOrderPlugin.js
+++ b/lib/optimize/OccurrenceModuleOrderPlugin.js
@@ -8,12 +8,19 @@
 const validateOptions = require("schema-utils");
 const schema = require("../../schemas/plugins/optimize/OccurrenceOrderModuleIdsPlugin.json");
 
+/** @typedef {import("../Compiler")} Compiler */
+/** @typedef {import("../ModuleReason")} ModuleReason */
+
 class OccurrenceOrderModuleIdsPlugin {
 	constructor(options = {}) {
 		validateOptions(schema, options, "Occurrence Order Module Ids Plugin");
 		this.options = options;
 	}
 
+	/**
+	 * @param {Compiler} compiler webpack compiler
+	 * @returns {void}
+	 */
 	apply(compiler) {
 		const prioritiseInitial = this.options.prioritiseInitial;
 		compiler.hooks.compilation.tap(
@@ -38,12 +45,23 @@ class OccurrenceOrderModuleIdsPlugin {
 							entryCountMap.set(m, entry);
 						}
 
+						/**
+						 * @param {number} sum sum of occurs
+						 * @param {ModuleReason} r module reason
+						 * @returns {number} count of occurs
+						 */
 						const countOccursInEntry = (sum, r) => {
 							if (!r.module) {
 								return sum;
 							}
 							return sum + initialChunkChunkMap.get(r.module);
 						};
+
+						/**
+						 * @param {number} sum sum of occurs
+						 * @param {ModuleReason} r module reason
+						 * @returns {number} count of occurs
+						 */
 						const countOccurs = (sum, r) => {
 							if (!r.module) {
 								return sum;
diff --git a/lib/optimize/SideEffectsFlagPlugin.js b/lib/optimize/SideEffectsFlagPlugin.js
index 68bc63656..fe88e2ba0 100644
--- a/lib/optimize/SideEffectsFlagPlugin.js
+++ b/lib/optimize/SideEffectsFlagPlugin.js
@@ -9,6 +9,7 @@ const mm = require("micromatch");
 const HarmonyExportImportedSpecifierDependency = require("../dependencies/HarmonyExportImportedSpecifierDependency");
 const HarmonyImportSpecifierDependency = require("../dependencies/HarmonyImportSpecifierDependency");
 
+/** @typedef {import("../Compiler")} Compiler */
 /** @typedef {import("../Dependency")} Dependency */
 /** @typedef {import("../Module")} Module */
 
@@ -19,6 +20,10 @@ const HarmonyImportSpecifierDependency = require("../dependencies/HarmonyImportS
  */
 
 class SideEffectsFlagPlugin {
+	/**
+	 * @param {Compiler} compiler webpack compiler
+	 * @returns {void}
+	 */
 	apply(compiler) {
 		compiler.hooks.normalModuleFactory.tap("SideEffectsFlagPlugin", nmf => {
 			nmf.hooks.module.tap("SideEffectsFlagPlugin", (module, data) => {