diff --git a/packages/webpack-config-composer/lib/constants.js b/packages/webpack-config-composer/lib/constants.js
new file mode 100644
index 000000000..feb14f554
--- /dev/null
+++ b/packages/webpack-config-composer/lib/constants.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  PARTIALS: Symbol("partials"),
+  PROFILES: Symbol("profiles")
+};
diff --git a/packages/webpack-config-composer/lib/index.js b/packages/webpack-config-composer/lib/index.js
index 23e379c49..7457612e2 100644
--- a/packages/webpack-config-composer/lib/index.js
+++ b/packages/webpack-config-composer/lib/index.js
@@ -7,11 +7,13 @@ const Partial = require("./partial");
 const Profile = require("./profile");
 const { getConcatMethod } = require("./concat-method");
 
+const { PARTIALS, PROFILES } = require("./constants");
+
 class WebpackConfigComposer {
   constructor(options) {
     options = options || {};
-    this._profiles = {};
-    this._partials = {};
+    this[PROFILES] = {};
+    this[PARTIALS] = {};
     if (options.profiles) {
       this.addProfiles(options.profiles);
     }
@@ -22,11 +24,11 @@ class WebpackConfigComposer {
   }
 
   get profiles() {
-    return this._profiles;
+    return this[PROFILES];
   }
 
   get partials() {
-    return this._partials;
+    return this[PARTIALS];
   }
 
   addProfiles(profiles) {
@@ -53,7 +55,7 @@ class WebpackConfigComposer {
       profile = new Profile(name, partials);
     }
 
-    this._profiles[name] = profile;
+    this[PROFILES][name] = profile;
 
     return profile;
   }
@@ -82,10 +84,10 @@ class WebpackConfigComposer {
   }
 
   _addPartial(name, data, addOpt) {
-    const exist = this._partials[name];
+    const exist = this[PARTIALS][name];
 
     if (!exist || _.get(addOpt, "method") === "replace") {
-      this._partials[name] = new Partial(name, data);
+      this[PARTIALS][name] = data instanceof Partial ? data : new Partial(name, data);
     } else {
       exist.merge(data, _.get(addOpt, "concatArray"));
     }
@@ -102,11 +104,18 @@ class WebpackConfigComposer {
   }
 
   getPartial(name) {
-    return this._partials[name];
+    return this[PARTIALS][name];
+  }
+
+  enablePartial(name, flag) {
+    const partial = this.getPartial(name);
+    if (partial) {
+      partial.enable = flag;
+    }
   }
 
   getProfile(name) {
-    return this._profiles[name];
+    return this[PROFILES][name];
   }
 
   compose(options, ...profiles) {
diff --git a/packages/webpack-config-composer/lib/partial.js b/packages/webpack-config-composer/lib/partial.js
index 32d318a5a..19eaa1b56 100644
--- a/packages/webpack-config-composer/lib/partial.js
+++ b/packages/webpack-config-composer/lib/partial.js
@@ -2,34 +2,49 @@
 
 const _ = require("lodash");
 const { getConcatMethod } = require("./concat-method");
+const assert = require("assert");
+
+const OVERRIDE = Symbol("override webpack config partial");
+const DATA = Symbol("webpack partial data");
 
 class Partial {
   constructor(name, data) {
     this._name = name;
-    this._data = Object.assign({ config: {}, options: {} }, data);
+    if (typeof data === "function") {
+      this[DATA] = { config: data };
+    } else {
+      this[DATA] = Object.assign({ config: {}, options: {} }, data);
+    }
+    this.setOverride();
   }
 
   set config(config) {
-    this._data.config = config;
+    this[DATA].config = config;
   }
 
   get config() {
-    return this._data.config;
+    return this[DATA].config;
   }
 
   set options(options) {
-    this._data.options = Object.assign({}, options);
+    this[DATA].options = Object.assign({}, options);
   }
 
   get options() {
-    return this._data.options;
+    return this[DATA].options;
   }
 
   merge(data, concatArray) {
-    _.mergeWith(this._data, data, getConcatMethod(concatArray));
+    _.mergeWith(this[DATA], data, getConcatMethod(concatArray));
+  }
+
+  setOverride(fn) {
+    this[OVERRIDE] = fn || _.identity;
   }
 
   compose(options) {
+    options = Object.assign({}, this.options, options);
+
     const config = this.config;
     const configType = typeof config;
 
@@ -38,7 +53,6 @@ class Partial {
     if (configType === "object") {
       ret = config;
     } else if (configType === "function") {
-      options = Object.assign({}, this.options, options);
       ret = config(options);
       if (typeof ret === "function") {
         ret = ret(options);
@@ -47,7 +61,9 @@ class Partial {
       throw new Error(`can't process config from Partial ${this._name}`);
     }
 
-    return ret;
+    const override = this[OVERRIDE](ret, options);
+
+    return override || ret;
   }
 }
 
diff --git a/packages/webpack-config-composer/lib/profile.js b/packages/webpack-config-composer/lib/profile.js
index b0fa14372..3b5fa4d62 100644
--- a/packages/webpack-config-composer/lib/profile.js
+++ b/packages/webpack-config-composer/lib/profile.js
@@ -1,9 +1,11 @@
 "use strict";
 
+const { PARTIALS } = require("./constants");
+
 class Profile {
   constructor(name, partials) {
     this._name = name;
-    this._partials = partials || {};
+    this[PARTIALS] = partials || {};
   }
 
   get name() {
@@ -11,19 +13,19 @@ class Profile {
   }
 
   get partials() {
-    return this._partials;
+    return this[PARTIALS];
   }
 
   setPartial(name, options) {
-    this._partials[name] = options || {};
+    this[PARTIALS][name] = options || {};
   }
 
   getPartial(name) {
-    return this._partials[name];
+    return this[PARTIALS][name];
   }
 
   delPartial(name) {
-    delete this._partials[name];
+    delete this[PARTIALS][name];
   }
 }
 
diff --git a/packages/xarc-app-dev/config/webpack/index.js b/packages/xarc-app-dev/config/webpack/index.js
index b7c07c685..9b6a15164 100644
--- a/packages/xarc-app-dev/config/webpack/index.js
+++ b/packages/xarc-app-dev/config/webpack/index.js
@@ -17,5 +17,6 @@ module.exports = {
   initWebpackConfigComposer,
   compose: generateConfig,
   env: profile,
-  options
+  options,
+  partials: require("./partials")
 };
diff --git a/packages/xarc-app-dev/config/webpack/partials/dll-entry.js b/packages/xarc-app-dev/config/webpack/partials/dll-entry.js
index 3c4b5b01e..b04d870f3 100644
--- a/packages/xarc-app-dev/config/webpack/partials/dll-entry.js
+++ b/packages/xarc-app-dev/config/webpack/partials/dll-entry.js
@@ -5,6 +5,6 @@ const AppMode = archetype.AppMode;
 const Path = require("path");
 const clientDllConfig = require(Path.resolve(AppMode.src.client, "dll.config.js"));
 
-module.exports = {
+module.exports = () => ({
   entry: clientDllConfig
-};
+});
diff --git a/packages/xarc-app-dev/config/webpack/partials/dll-output.js b/packages/xarc-app-dev/config/webpack/partials/dll-output.js
index f3ae1f566..208c6f520 100644
--- a/packages/xarc-app-dev/config/webpack/partials/dll-output.js
+++ b/packages/xarc-app-dev/config/webpack/partials/dll-output.js
@@ -2,10 +2,10 @@
 
 const Path = require("path");
 
-module.exports = {
+module.exports = () => ({
   output: {
     path: Path.resolve("dll/js"),
     filename: "[name].bundle.[hash].js",
     library: "[name]_[hash]"
   }
-};
+});
diff --git a/packages/xarc-app-dev/config/webpack/partials/entry.js b/packages/xarc-app-dev/config/webpack/partials/entry.js
index cfa65cdd3..1799ef9d5 100644
--- a/packages/xarc-app-dev/config/webpack/partials/entry.js
+++ b/packages/xarc-app-dev/config/webpack/partials/entry.js
@@ -211,4 +211,4 @@ if (module.hot) {
   return partial;
 }
 
-module.exports = makeEntryPartial();
+module.exports = makeEntryPartial;
diff --git a/packages/xarc-app-dev/config/webpack/partials/index.js b/packages/xarc-app-dev/config/webpack/partials/index.js
index 71f9bd8a3..73266d6e5 100644
--- a/packages/xarc-app-dev/config/webpack/partials/index.js
+++ b/packages/xarc-app-dev/config/webpack/partials/index.js
@@ -2,6 +2,7 @@
 
 const Fs = require("fs");
 const assert = require("assert");
+const Partial = require("webpack-config-composer/lib/partial");
 
 //
 // This specifies a general order of partials to be applied.
@@ -50,12 +51,11 @@ const files = Fs.readdirSync(__dirname)
   .filter(x => x !== "index.js")
   .map(x => x.substr(0, x.length - 3));
 
-module.exports = {
-  orders,
-  partials: files.reduce((a, p) => {
-    const k = `_${p}`;
-    assert(orders.indexOf(k) >= 0, `No default order specified for partial ${p}`);
-    a[k] = { config: () => require(`./${p}`) };
-    return a;
-  }, {})
-};
+const partials = files.reduce((a, p) => {
+  const k = `_${p}`;
+  assert(orders.indexOf(k) >= 0, `No default order specified for partial ${p}`);
+  a[k] = new Partial(k, { config: () => require(`./${p}`) });
+  return a;
+}, {});
+
+module.exports = partials;
diff --git a/packages/xarc-app-dev/config/webpack/partials/output.js b/packages/xarc-app-dev/config/webpack/partials/output.js
index 7acf08b28..f222ef2e0 100644
--- a/packages/xarc-app-dev/config/webpack/partials/output.js
+++ b/packages/xarc-app-dev/config/webpack/partials/output.js
@@ -26,7 +26,7 @@ const getOutputPath = () => {
   }
 };
 
-module.exports = {
+module.exports = () => ({
   output: {
     path: getOutputPath(),
     pathinfo: inspectpack, // Enable path information for inspectpack
@@ -36,4 +36,4 @@ module.exports = {
       : "[contenthash].[name].js",
     filename: getOutputFilename()
   }
-};
+});
diff --git a/packages/xarc-app-dev/config/webpack/partials/resolve-loader.js b/packages/xarc-app-dev/config/webpack/partials/resolve-loader.js
index f838bbff9..6d6bc0817 100644
--- a/packages/xarc-app-dev/config/webpack/partials/resolve-loader.js
+++ b/packages/xarc-app-dev/config/webpack/partials/resolve-loader.js
@@ -5,7 +5,7 @@ const Path = require("path");
 const ModuleResolver = require("electrode-node-resolver/lib/webpack-plugin");
 const archetype = require("@xarc/app/config/archetype");
 
-module.exports = {
+module.exports = () => ({
   resolveLoader: {
     symlinks: !archetype.webpack.preserveSymlinks,
     modules: [Path.resolve("lib"), process.cwd()]
@@ -13,4 +13,4 @@ module.exports = {
       .filter(identity),
     plugins: [new ModuleResolver("module", "resolve", archetype.devDir, undefined)]
   }
-};
+});
diff --git a/packages/xarc-app-dev/config/webpack/partials/resolve.js b/packages/xarc-app-dev/config/webpack/partials/resolve.js
index 82452b148..692806677 100644
--- a/packages/xarc-app-dev/config/webpack/partials/resolve.js
+++ b/packages/xarc-app-dev/config/webpack/partials/resolve.js
@@ -53,4 +53,4 @@ if (AppMode.hasSubApps) {
   resolve.mainFields = ["module", "browser", "main"];
 }
 
-module.exports = { resolve };
+module.exports = () => ({ resolve });
diff --git a/packages/xarc-app-dev/config/webpack/partials/subapp-chunks.js b/packages/xarc-app-dev/config/webpack/partials/subapp-chunks.js
index b659a68eb..49f0cff5c 100644
--- a/packages/xarc-app-dev/config/webpack/partials/subapp-chunks.js
+++ b/packages/xarc-app-dev/config/webpack/partials/subapp-chunks.js
@@ -1,9 +1,6 @@
 "use strict";
 
 const Crypto = require("crypto");
-const { AppMode, webpack } = require("@xarc/app/config/archetype");
-
-const config = {};
 
 const splitMap = {};
 
@@ -20,53 +17,65 @@ function hashChunks(mod, chunks, key) {
   return `${key}~${digest}`;
 }
 
-if (AppMode.hasSubApps && webpack.minimizeSubappChunks) {
-  config.optimization = {
-    runtimeChunk: "single",
-    splitChunks: {
-      cacheGroups: {
-        common: {
-          chunks: "all",
-          minChunks: 2,
-          enforce: true,
-          name: "common"
+function makeConfig() {
+  const { AppMode, webpack } = require("@xarc/app/config/archetype");
+
+  const config = {};
+
+  if (!AppMode.hasSubApps) {
+    return config;
+  }
+
+  if (webpack.minimizeSubappChunks) {
+    config.optimization = {
+      runtimeChunk: "single",
+      splitChunks: {
+        cacheGroups: {
+          common: {
+            chunks: "all",
+            minChunks: 2,
+            enforce: true,
+            name: "common"
+          }
         }
       }
-    }
-  };
-} else if (AppMode.hasSubApps) {
-  // use webpack splitChunks optimization to automatically put modules
-  // shared by subapps into common bundles.
-  // The common bundles will be determined by the splitChunks parameters.
-  // The filename has the pattern of hex-sum.bundle1~bundle2~bundle#.js
-  // https://webpack.js.org/plugins/split-chunks-plugin/
-  config.optimization = {
-    runtimeChunk: "single",
-    splitChunks: {
-      chunks: "all",
-      minSize: 30 * 1024,
-      maxSize: 0,
-      minChunks: 2,
-      maxAsyncRequests: 500,
-      maxInitialRequests: 500,
-      automaticNameDelimiter: "~",
-      automaticNameMaxLength: 250,
-      cacheGroups: {
-        vendors: {
-          test: /[\\/]node_modules[\\/]/,
-          // https://webpack.js.org/plugins/split-chunks-plugin/#splitchunksname
-          name: hashChunks,
-          priority: -10,
-          reuseExistingChunk: true
-        },
-        shared: {
-          name: hashChunks,
-          priority: -20,
-          reuseExistingChunk: true
+    };
+  } else {
+    // use webpack splitChunks optimization to automatically put modules
+    // shared by subapps into common bundles.
+    // The common bundles will be determined by the splitChunks parameters.
+    // The filename has the pattern of hex-sum.bundle1~bundle2~bundle#.js
+    // https://webpack.js.org/plugins/split-chunks-plugin/
+    config.optimization = {
+      runtimeChunk: "single",
+      splitChunks: {
+        chunks: "all",
+        minSize: 30 * 1024,
+        maxSize: 0,
+        minChunks: 2,
+        maxAsyncRequests: 500,
+        maxInitialRequests: 500,
+        automaticNameDelimiter: "~",
+        automaticNameMaxLength: 250,
+        cacheGroups: {
+          vendors: {
+            test: /[\\/]node_modules[\\/]/,
+            // https://webpack.js.org/plugins/split-chunks-plugin/#splitchunksname
+            name: hashChunks,
+            priority: -10,
+            reuseExistingChunk: true
+          },
+          shared: {
+            name: hashChunks,
+            priority: -20,
+            reuseExistingChunk: true
+          }
         }
       }
-    }
-  };
+    };
+  }
+
+  return config;
 }
 
-module.exports = config;
+module.exports = makeConfig;
diff --git a/packages/xarc-app-dev/config/webpack/partials/test-base.js b/packages/xarc-app-dev/config/webpack/partials/test-base.js
index 6e2732057..6124fd015 100644
--- a/packages/xarc-app-dev/config/webpack/partials/test-base.js
+++ b/packages/xarc-app-dev/config/webpack/partials/test-base.js
@@ -2,7 +2,7 @@
 
 const Path = require("path");
 
-module.exports = {
+module.exports = () => ({
   module: {
     /*
      * This prevents webpack from running its parsers on any sinon files. Sinon breaks when it is
@@ -34,4 +34,4 @@ module.exports = {
     "react/lib/ExecutionEnvironment": true,
     "react/lib/ReactContext": true
   }
-};
+});
diff --git a/packages/xarc-app-dev/config/webpack/partials/test-output.js b/packages/xarc-app-dev/config/webpack/partials/test-output.js
index d90813081..9fdd7f21c 100644
--- a/packages/xarc-app-dev/config/webpack/partials/test-output.js
+++ b/packages/xarc-app-dev/config/webpack/partials/test-output.js
@@ -1,9 +1,9 @@
 "use strict";
 
-module.exports = {
+module.exports = () => ({
   output: {
     path: process.cwd(),
     filename: "[name].bundle.js",
     publicPath: "/assets/"
   }
-};
+});
diff --git a/packages/xarc-app-dev/config/webpack/partials/test-resolve.js b/packages/xarc-app-dev/config/webpack/partials/test-resolve.js
index e743ed720..f11063ad3 100644
--- a/packages/xarc-app-dev/config/webpack/partials/test-resolve.js
+++ b/packages/xarc-app-dev/config/webpack/partials/test-resolve.js
@@ -1,7 +1,7 @@
 "use strict";
 
 const optionalRequire = require("optional-require")(require);
-module.exports = {
+module.exports = () => ({
   resolve: {
     alias: {
       // Allow root import of `src/FOO` from ROOT/src.
@@ -9,4 +9,4 @@ module.exports = {
       sinon: optionalRequire.resolve("sinon/pkg/sinon") || ""
     }
   }
-};
+});
diff --git a/packages/xarc-app-dev/config/webpack/util/generate-config.js b/packages/xarc-app-dev/config/webpack/util/generate-config.js
index 733cff110..f685aaac8 100644
--- a/packages/xarc-app-dev/config/webpack/util/generate-config.js
+++ b/packages/xarc-app-dev/config/webpack/util/generate-config.js
@@ -3,7 +3,7 @@
 /* eslint-disable no-unused-expressions */
 
 const xsh = require("xsh");
-const partialConfigs = require("../partials");
+const partials = require("../partials");
 const WebpackConfigComposer = require("webpack-config-composer");
 const optionalRequire = require("optional-require")(require);
 const Path = require("path");
@@ -69,7 +69,7 @@ function initWebpackConfigComposer(options) {
 
     options.profiles && composer.addProfiles(options.profiles);
     composer.addProfile("user", {});
-    composer.addPartials(partialConfigs.partials);
+    composer.addPartials(partials);
     options.partials && composer.addPartials(options.partials);
   }