diff --git a/packager/src/AssetServer/index.js b/packager/src/AssetServer/index.js
index 1688a599d..c18caa3af 100644
--- a/packager/src/AssetServer/index.js
+++ b/packager/src/AssetServer/index.js
@@ -5,16 +5,20 @@
  * This source code is licensed under the BSD-style license found in the
  * LICENSE file in the root directory of this source tree. An additional grant
  * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
  */
+
 'use strict';
 
 const crypto = require('crypto');
-const declareOpts = require('../lib/declareOpts');
 const denodeify = require('denodeify');
 const fs = require('fs');
 const getAssetDataFromName = require('../node-haste').getAssetDataFromName;
 const path = require('path');
 
+import type {AssetData} from '../node-haste/lib/getAssetDataFromName';
+
 const createTimeoutPromise = timeout => new Promise((resolve, reject) => {
   setTimeout(reject, timeout, 'fs operation timeout');
 });
@@ -33,27 +37,24 @@ const stat = timeoutableDenodeify(fs.stat, FS_OP_TIMEOUT);
 const readDir = timeoutableDenodeify(fs.readdir, FS_OP_TIMEOUT);
 const readFile = timeoutableDenodeify(fs.readFile, FS_OP_TIMEOUT);
 
-const validateOpts = declareOpts({
-  projectRoots: {
-    type: 'array',
-    required: true,
-  },
-  assetExts: {
-    type: 'array',
-    required: true,
-  },
-});
-
 class AssetServer {
-  constructor(options) {
-    const opts = validateOpts(options);
-    this._roots = opts.projectRoots;
-    this._assetExts = opts.assetExts;
+
+  _roots: $ReadOnlyArray<string>;
+  _assetExts: $ReadOnlyArray<string>;
+  _hashes: Map<?string, string>;
+  _files: Map<string, string>;
+
+  constructor(options: {|
+    +assetExts: $ReadOnlyArray<string>,
+    +projectRoots: $ReadOnlyArray<string>,
+  |}) {
+    this._roots = options.projectRoots;
+    this._assetExts = options.assetExts;
     this._hashes = new Map();
     this._files = new Map();
   }
 
-  get(assetPath, platform = null) {
+  get(assetPath: string, platform: ?string = null): Promise<Buffer> {
     const assetData = getAssetDataFromName(assetPath, new Set([platform]));
     return this._getAssetRecord(assetPath, platform).then(record => {
       for (let i = 0; i < record.scales.length; i++) {
@@ -66,39 +67,41 @@ class AssetServer {
     });
   }
 
-  getAssetData(assetPath, platform = null) {
+  getAssetData(assetPath: string, platform: ?string = null): Promise<{|
+    files: Array<string>,
+    hash: string,
+    name: string,
+    scales: Array<number>,
+    type: string,
+  |}> {
     const nameData = getAssetDataFromName(assetPath, new Set([platform]));
-    const data = {
-      name: nameData.name,
-      type: nameData.type,
-    };
+    const {name, type} = nameData;
 
     return this._getAssetRecord(assetPath, platform).then(record => {
-      data.scales = record.scales;
-      data.files = record.files;
+      const {scales, files} = record;
 
-      if (this._hashes.has(assetPath)) {
-        data.hash = this._hashes.get(assetPath);
-        return data;
+      const hash = this._hashes.get(assetPath);
+      if (hash != null) {
+        return {files, hash, name, scales, type};
       }
 
       return new Promise((resolve, reject) => {
-        const hash = crypto.createHash('md5');
-        hashFiles(data.files.slice(), hash, error => {
+        const hasher = crypto.createHash('md5');
+        hashFiles(files.slice(), hasher, error => {
           if (error) {
             reject(error);
           } else {
-            data.hash = hash.digest('hex');
-            this._hashes.set(assetPath, data.hash);
-            data.files.forEach(f => this._files.set(f, assetPath));
-            resolve(data);
+            const freshHash = hasher.digest('hex');
+            this._hashes.set(assetPath, freshHash);
+            files.forEach(f => this._files.set(f, assetPath));
+            resolve({files, hash: freshHash, name, scales, type});
           }
         });
       });
     });
   }
 
-  onFileChange(type, filePath) {
+  onFileChange(type: string, filePath: string) {
     this._hashes.delete(this._files.get(filePath));
   }
 
@@ -113,7 +116,10 @@ class AssetServer {
    * 4. Then try to pick platform-specific asset records
    * 5. Then pick the closest resolution (rounding up) to the requested one
    */
-  _getAssetRecord(assetPath, platform = null) {
+  _getAssetRecord(assetPath: string, platform: ?string = null): Promise<{|
+    files: Array<string>,
+    scales: Array<number>,
+  |}> {
     const filename = path.basename(assetPath);
 
     return (
@@ -135,14 +141,15 @@ class AssetServer {
 
         let record;
         if (platform != null) {
-          record = map[getAssetKey(assetData.assetName, platform)] ||
-                   map[assetData.assetName];
+          record = map.get(getAssetKey(assetData.assetName, platform)) ||
+                   map.get(assetData.assetName);
         } else {
-          record = map[assetData.assetName];
+          record = map.get(assetData.assetName);
         }
 
         if (!record) {
           throw new Error(
+            /* $FlowFixMe: platform can be null */
             `Asset not found: ${assetPath} for platform: ${platform}`
           );
         }
@@ -152,7 +159,7 @@ class AssetServer {
     );
   }
 
-  _findRoot(roots, dir, debugInfoFile) {
+  _findRoot(roots: $ReadOnlyArray<string>, dir: string, debugInfoFile: string): Promise<string> {
     return Promise.all(
       roots.map(root => {
         const absRoot = path.resolve(root);
@@ -185,18 +192,23 @@ class AssetServer {
     });
   }
 
-  _buildAssetMap(dir, files, platform) {
-    const assets = files.map(this._getAssetDataFromName.bind(this, new Set([platform])));
-    const map = Object.create(null);
+  _buildAssetMap(dir: string, files: $ReadOnlyArray<string>, platform: ?string): Map<string, {|
+    files: Array<string>,
+    scales: Array<number>,
+  |}> {
+    const platforms = new Set(platform != null ? [platform] : []);
+    const assets = files.map(this._getAssetDataFromName.bind(this, platforms));
+    const map = new Map();
     assets.forEach(function(asset, i) {
       const file = files[i];
       const assetKey = getAssetKey(asset.assetName, asset.platform);
-      let record = map[assetKey];
+      let record = map.get(assetKey);
       if (!record) {
-        record = map[assetKey] = {
+        record = {
           scales: [],
           files: [],
         };
+        map.set(assetKey, record);
       }
 
       let insertIndex;
@@ -214,8 +226,8 @@ class AssetServer {
     return map;
   }
 
-  _getAssetDataFromName(platform, file) {
-    return getAssetDataFromName(file, platform);
+  _getAssetDataFromName(platforms: Set<string>, file: string): AssetData {
+    return getAssetDataFromName(file, platforms);
   }
 }
 
diff --git a/packager/src/Bundler/index.js b/packager/src/Bundler/index.js
index eb0252eb2..98a426543 100644
--- a/packager/src/Bundler/index.js
+++ b/packager/src/Bundler/index.js
@@ -59,18 +59,18 @@ export type GetTransformOptions = (
   getDependencies: string => Promise<Array<string>>,
 ) => Promise<ExtraTransformOptions>;
 
-type Asset = {
-  __packager_asset: boolean,
-  fileSystemLocation: string,
-  httpServerLocation: string,
-  width: ?number,
-  height: ?number,
-  scales: number,
-  files: Array<string>,
-  hash: string,
-  name: string,
-  type: string,
-};
+type Asset = {|
+  +__packager_asset: boolean,
+  +fileSystemLocation: string,
+  +httpServerLocation: string,
+  +width: ?number,
+  +height: ?number,
+  +scales: Array<number>,
+  +files: Array<string>,
+  +hash: string,
+  +name: string,
+  +type: string,
+|};
 
 const sizeOf = denodeify(imageSize);
 
@@ -696,7 +696,7 @@ class Bundler {
       return {
         asset,
         code,
-        meta: {dependencies, dependencyOffsets},
+        meta: {dependencies, dependencyOffsets, preloaded: null},
       };
     });
   }
diff --git a/packager/src/Server/index.js b/packager/src/Server/index.js
index 98a6066e3..198452d09 100644
--- a/packager/src/Server/index.js
+++ b/packager/src/Server/index.js
@@ -428,7 +428,7 @@ class Server {
   _rangeRequestMiddleware(
     req: IncomingMessage,
     res: ServerResponse,
-    data: string,
+    data: string | Buffer,
     assetPath: string,
   ) {
     if (req.headers && req.headers.range) {
diff --git a/packager/src/node-haste/lib/getAssetDataFromName.js b/packager/src/node-haste/lib/getAssetDataFromName.js
index e41279188..05e816dd3 100644
--- a/packager/src/node-haste/lib/getAssetDataFromName.js
+++ b/packager/src/node-haste/lib/getAssetDataFromName.js
@@ -14,13 +14,15 @@
 const getPlatformExtension = require('./getPlatformExtension');
 const path = require('path');
 
-function getAssetDataFromName(filename: string, platforms: Set<string>): {|
+export type AssetData = {|
   assetName: string,
   name: string,
   platform: ?string,
   resolution: number,
   type: string,
-|} {
+|};
+
+function getAssetDataFromName(filename: string, platforms: Set<string>): AssetData {
   const ext = path.extname(filename);
   const platformExt = getPlatformExtension(filename, platforms);