diff --git a/lib/Compilation.js b/lib/Compilation.js
index 0330973c9..ae58de553 100644
--- a/lib/Compilation.js
+++ b/lib/Compilation.js
@@ -192,18 +192,6 @@ const bySetSize = (a, b) => {
 	return a.size - b.size;
 };
 
-/**
- * @template T
- * @param {T[]} arr array of elements to iterate over
- * @param {function(T): void} fn callback applied to each element
- * @returns {void}
- */
-const iterationOfArrayCallback = (arr, fn) => {
-	for (let index = 0; index < arr.length; index++) {
-		fn(arr[index]);
-	}
-};
-
 /**
  * @template T
  * @param {Set<T>} set set to add items to
@@ -787,10 +775,10 @@ class Compilation {
 		const processDependenciesBlock = block => {
 			if (block.dependencies) {
 				currentBlock = block;
-				iterationOfArrayCallback(block.dependencies, processDependency);
+				for (const dep of block.dependencies) processDependency(dep);
 			}
 			if (block.blocks) {
-				iterationOfArrayCallback(block.blocks, processDependenciesBlock);
+				for (const b of block.blocks) processDependenciesBlock(b);
 			}
 		};
 
@@ -1633,11 +1621,11 @@ class Compilation {
 		 */
 		const assignDepthToDependencyBlock = block => {
 			if (block.dependencies) {
-				iterationOfArrayCallback(block.dependencies, assignDepthToDependency);
+				for (const dep of block.dependencies) assignDepthToDependency(dep);
 			}
 
 			if (block.blocks) {
-				iterationOfArrayCallback(block.blocks, assignDepthToDependencyBlock);
+				for (const b of block.blocks) assignDepthToDependencyBlock(b);
 			}
 		};
 
@@ -1736,11 +1724,11 @@ class Compilation {
 				blockInfoBlocks = [];
 
 				if (block.dependencies) {
-					iterationOfArrayCallback(block.dependencies, iteratorDependency);
+					for (const dep of block.dependencies) iteratorDependency(dep);
 				}
 
 				if (block.blocks) {
-					iterationOfArrayCallback(block.blocks, iteratorBlockPrepare);
+					for (const b of block.blocks) iteratorBlockPrepare(b);
 				}
 
 				const blockInfo = {
@@ -1944,7 +1932,7 @@ class Compilation {
 						}
 
 						// Traverse all Blocks
-						iterationOfArrayCallback(blockInfo.blocks, iteratorBlock);
+						for (const block of blockInfo.blocks) iteratorBlock(block);
 
 						if (blockInfo.blocks.length > 0 && module !== block) {
 							blocksWithNestedBlocks.add(block);
@@ -2150,13 +2138,13 @@ class Compilation {
 		};
 
 		if (block.blocks) {
-			iterationOfArrayCallback(block.blocks, block =>
-				this.removeReasonsOfDependencyBlock(module, block)
-			);
+			for (const b of block.blocks) {
+				this.removeReasonsOfDependencyBlock(module, b);
+			}
 		}
 
 		if (block.dependencies) {
-			iterationOfArrayCallback(block.dependencies, iteratorDependency);
+			for (const dep of block.dependencies) iteratorDependency(dep);
 		}
 	}
 
@@ -2207,7 +2195,7 @@ class Compilation {
 		}
 
 		if (block.dependencies) {
-			iterationOfArrayCallback(block.dependencies, iteratorDependency);
+			for (const dep of block.dependencies) iteratorDependency(dep);
 		}
 	}
 
diff --git a/lib/optimize/SplitChunksPlugin.js b/lib/optimize/SplitChunksPlugin.js
index 285db357a..567571514 100644
--- a/lib/optimize/SplitChunksPlugin.js
+++ b/lib/optimize/SplitChunksPlugin.js
@@ -250,7 +250,12 @@ const normalizeSizes = value => {
  * @returns {SplitChunksSizes} the merged sizes
  */
 const mergeSizes = (...sizes) => {
-	return Object.assign({}, ...sizes.map(normalizeSizes).reverse());
+	/** @type {SplitChunksSizes} */
+	let merged = {};
+	for (let i = sizes.length - 1; i >= 0; i--) {
+		merged = Object.assign(merged, normalizeSizes(sizes[i]));
+	}
+	return merged;
 };
 
 /**
diff --git a/package.json b/package.json
index 3d9f63700..7513e758c 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,7 @@
     "ajv": "^6.1.0",
     "ajv-keywords": "^3.1.0",
     "chrome-trace-event": "^1.0.0",
-    "enhanced-resolve": "5.0.0-beta.1",
+    "enhanced-resolve": "5.0.0-beta.2",
     "eslint-scope": "^4.0.0",
     "events": "^3.0.0",
     "find-cache-dir": "^2.1.0",
@@ -24,7 +24,7 @@
     "loader-utils": "^1.1.0",
     "neo-async": "^2.6.0",
     "schema-utils": "^1.0.0",
-    "tapable": "2.0.0-beta.5",
+    "tapable": "2.0.0-beta.8",
     "terser-webpack-plugin": "^1.2.1",
     "watchpack": "2.0.0-beta.6",
     "webpack-sources": "2.0.0-beta.1"
diff --git a/yarn.lock b/yarn.lock
index 01eb96ac8..af5ecd19b 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1591,13 +1591,13 @@ end-of-stream@^1.0.0, end-of-stream@^1.1.0:
   dependencies:
     once "^1.4.0"
 
-enhanced-resolve@5.0.0-beta.1:
-  version "5.0.0-beta.1"
-  resolved "https://registry.yarnpkg.com/enhanced-resolve/-/enhanced-resolve-5.0.0-beta.1.tgz#600c242ec84a31f7198e165ea08143eef2cc3a04"
-  integrity sha512-dlCyQrjJDL/RJzVWzZkrO5aL8EYCGpMvqGv5IPwaVCO8yLMs+rQuuMczeOxYNj0hD2DAtOGAfvocgDkzbNCmDg==
+enhanced-resolve@5.0.0-beta.2:
+  version "5.0.0-beta.2"
+  resolved "https://registry.yarnpkg.com/enhanced-resolve/-/enhanced-resolve-5.0.0-beta.2.tgz#9dfd00b7d73e7d6e0acab9e1f54241a557edbe8d"
+  integrity sha512-qo97XNV7JrYZR9eaFRPfKtOtiF1RBTGIx9v+j5DttaZyAhwgXnhs69YYTzEKgQpiOW8snnAiVdp5/eu+d3/55g==
   dependencies:
     graceful-fs "^4.2.0"
-    tapable "^2.0.0-beta"
+    tapable "^2.0.0-beta.8"
 
 errno@^0.1.1, errno@^0.1.3, errno@~0.1.7:
   version "0.1.7"
@@ -5336,10 +5336,10 @@ table@^5.2.3:
     slice-ansi "^2.1.0"
     string-width "^3.0.0"
 
-tapable@2.0.0-beta.5, tapable@^2.0.0-beta:
-  version "2.0.0-beta.5"
-  resolved "https://registry.yarnpkg.com/tapable/-/tapable-2.0.0-beta.5.tgz#51def4d94c58ad8fadf00cac7661216502fe9c70"
-  integrity sha512-P4o84kC8CD66ZuCs6noh3QLU2ZuaBvMl0yCmp9rr0GXZyIfLd1sB2ZvJZjitQgfds8GDKRLmiiAcssr2bEHQ0A==
+tapable@2.0.0-beta.8, tapable@^2.0.0-beta.8:
+  version "2.0.0-beta.8"
+  resolved "https://registry.yarnpkg.com/tapable/-/tapable-2.0.0-beta.8.tgz#0a8d42f6895d43d5a895de15d9a9e3e425f72a0a"
+  integrity sha512-7qMajFcHb2O+aWufLoAvKhEehIwikXUTH1s8RP4R5gSYMIB0Tmypp+J90EtSNVbIlI7oB0Oz8ZlpJUJlZ5owxQ==
 
 terser-webpack-plugin@^1.2.1:
   version "1.3.0"