From 9f68b2250d283f451bc5a8fb6afd227fbeccd333 Mon Sep 17 00:00:00 2001
From: David Chin <davidchin.yf@gmail.com>
Date: Fri, 19 Jan 2018 12:30:46 +1100
Subject: [PATCH 1/3] chore(common): CHECKOUT-2507 Add `.ts` extension to files
 in `DataStore` module

---
 .../{combine-reducers.spec.js => combine-reducers.spec.ts}        | 0
 src/data-store/{combine-reducers.js => combine-reducers.ts}       | 0
 .../{compose-reducers.spec.js => compose-reducers.spec.ts}        | 0
 src/data-store/{compose-reducers.js => compose-reducers.ts}       | 0
 src/data-store/{create-action.spec.js => create-action.spec.ts}   | 0
 src/data-store/{create-action.js => create-action.ts}             | 0
 src/data-store/{create-data-store.js => create-data-store.ts}     | 0
 .../{create-error-action.spec.js => create-error-action.spec.ts}  | 0
 src/data-store/{create-error-action.js => create-error-action.ts} | 0
 src/data-store/{data-store.spec.js => data-store.spec.ts}         | 0
 src/data-store/{data-store.js => data-store.ts}                   | 0
 src/data-store/{deep-freeze.spec.js => deep-freeze.spec.ts}       | 0
 src/data-store/{deep-freeze.js => deep-freeze.ts}                 | 0
 src/data-store/{index.js => index.ts}                             | 0
 .../{noop-action-transformer.js => noop-action-transformer.ts}    | 0
 .../{noop-state-transformer.js => noop-state-transformer.ts}      | 0
 16 files changed, 0 insertions(+), 0 deletions(-)
 rename src/data-store/{combine-reducers.spec.js => combine-reducers.spec.ts} (100%)
 rename src/data-store/{combine-reducers.js => combine-reducers.ts} (100%)
 rename src/data-store/{compose-reducers.spec.js => compose-reducers.spec.ts} (100%)
 rename src/data-store/{compose-reducers.js => compose-reducers.ts} (100%)
 rename src/data-store/{create-action.spec.js => create-action.spec.ts} (100%)
 rename src/data-store/{create-action.js => create-action.ts} (100%)
 rename src/data-store/{create-data-store.js => create-data-store.ts} (100%)
 rename src/data-store/{create-error-action.spec.js => create-error-action.spec.ts} (100%)
 rename src/data-store/{create-error-action.js => create-error-action.ts} (100%)
 rename src/data-store/{data-store.spec.js => data-store.spec.ts} (100%)
 rename src/data-store/{data-store.js => data-store.ts} (100%)
 rename src/data-store/{deep-freeze.spec.js => deep-freeze.spec.ts} (100%)
 rename src/data-store/{deep-freeze.js => deep-freeze.ts} (100%)
 rename src/data-store/{index.js => index.ts} (100%)
 rename src/data-store/{noop-action-transformer.js => noop-action-transformer.ts} (100%)
 rename src/data-store/{noop-state-transformer.js => noop-state-transformer.ts} (100%)

diff --git a/src/data-store/combine-reducers.spec.js b/src/data-store/combine-reducers.spec.ts
similarity index 100%
rename from src/data-store/combine-reducers.spec.js
rename to src/data-store/combine-reducers.spec.ts
diff --git a/src/data-store/combine-reducers.js b/src/data-store/combine-reducers.ts
similarity index 100%
rename from src/data-store/combine-reducers.js
rename to src/data-store/combine-reducers.ts
diff --git a/src/data-store/compose-reducers.spec.js b/src/data-store/compose-reducers.spec.ts
similarity index 100%
rename from src/data-store/compose-reducers.spec.js
rename to src/data-store/compose-reducers.spec.ts
diff --git a/src/data-store/compose-reducers.js b/src/data-store/compose-reducers.ts
similarity index 100%
rename from src/data-store/compose-reducers.js
rename to src/data-store/compose-reducers.ts
diff --git a/src/data-store/create-action.spec.js b/src/data-store/create-action.spec.ts
similarity index 100%
rename from src/data-store/create-action.spec.js
rename to src/data-store/create-action.spec.ts
diff --git a/src/data-store/create-action.js b/src/data-store/create-action.ts
similarity index 100%
rename from src/data-store/create-action.js
rename to src/data-store/create-action.ts
diff --git a/src/data-store/create-data-store.js b/src/data-store/create-data-store.ts
similarity index 100%
rename from src/data-store/create-data-store.js
rename to src/data-store/create-data-store.ts
diff --git a/src/data-store/create-error-action.spec.js b/src/data-store/create-error-action.spec.ts
similarity index 100%
rename from src/data-store/create-error-action.spec.js
rename to src/data-store/create-error-action.spec.ts
diff --git a/src/data-store/create-error-action.js b/src/data-store/create-error-action.ts
similarity index 100%
rename from src/data-store/create-error-action.js
rename to src/data-store/create-error-action.ts
diff --git a/src/data-store/data-store.spec.js b/src/data-store/data-store.spec.ts
similarity index 100%
rename from src/data-store/data-store.spec.js
rename to src/data-store/data-store.spec.ts
diff --git a/src/data-store/data-store.js b/src/data-store/data-store.ts
similarity index 100%
rename from src/data-store/data-store.js
rename to src/data-store/data-store.ts
diff --git a/src/data-store/deep-freeze.spec.js b/src/data-store/deep-freeze.spec.ts
similarity index 100%
rename from src/data-store/deep-freeze.spec.js
rename to src/data-store/deep-freeze.spec.ts
diff --git a/src/data-store/deep-freeze.js b/src/data-store/deep-freeze.ts
similarity index 100%
rename from src/data-store/deep-freeze.js
rename to src/data-store/deep-freeze.ts
diff --git a/src/data-store/index.js b/src/data-store/index.ts
similarity index 100%
rename from src/data-store/index.js
rename to src/data-store/index.ts
diff --git a/src/data-store/noop-action-transformer.js b/src/data-store/noop-action-transformer.ts
similarity index 100%
rename from src/data-store/noop-action-transformer.js
rename to src/data-store/noop-action-transformer.ts
diff --git a/src/data-store/noop-state-transformer.js b/src/data-store/noop-state-transformer.ts
similarity index 100%
rename from src/data-store/noop-state-transformer.js
rename to src/data-store/noop-state-transformer.ts

From 293e5e14eba220d9556e3ea931f2a2406af78bef Mon Sep 17 00:00:00 2001
From: David Chin <davidchin.yf@gmail.com>
Date: Thu, 18 Jan 2018 14:33:06 +1100
Subject: [PATCH 2/3] chore(common): CHECKOUT-2507 Add `tslint` to lint
 TypeScript files

We are using the default configuration provided by `tslint`. We have
added some overrides in order to match with the configuration we have
for JavaScript files (enforced by `eslint`). We will need to revisit the
rules some time in the future.
---
 package.json |  5 ++++-
 tslint.json  | 27 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 tslint.json

diff --git a/package.json b/package.json
index 0b496b348d..cd36d632ed 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,9 @@
     "precompile": "rm -rf lib",
     "compile": "tsc --outDir lib",
     "compile:watch": "yarn compile -- --watch",
-    "lint": "eslint src --config eslintrc.json",
+    "lint": "yarn lint:js && yarn lint:ts",
+    "lint:js": "eslint src --config eslintrc.json",
+    "lint:ts": "tslint src/**/*.ts --config tslint.json",
     "prerelease": "git fetch --tags && yarn validate-dependencies && yarn validate-commits && yarn build",
     "release": "git add dist lib && standard-version -a",
     "test": "jest --config jest-config.js",
@@ -60,6 +62,7 @@
     "standard-version": "^4.2.0",
     "ts-jest": "^21.2.3",
     "ts-loader": "^3.2.0",
+    "tslint": "^5.9.1",
     "typescript": "^2.6.2",
     "typescript-eslint-parser": "^9.0.1",
     "uglifyjs-webpack-plugin": "^1.1.1",
diff --git a/tslint.json b/tslint.json
new file mode 100644
index 0000000000..3822098852
--- /dev/null
+++ b/tslint.json
@@ -0,0 +1,27 @@
+{
+    "extends": "tslint:recommended",
+    "rules": {
+        "arrow-parens": false,
+        "grouped-imports": false,
+        "interface-name": [true, "never-prefix"],
+        "max-line-length": false,
+        "member-access": [true, "no-public"],
+        "no-empty": false,
+        "no-shadowed-variable": false,
+        "object-literal-sort-keys": false,
+        "ordered-imports": false,
+        "quotemark": [true, "single"],
+        "trailing-comma": [
+            true,
+            {
+                "multiline": {
+                    "arrays": "always",
+                    "functions": "never",
+                    "objects": "always",
+                    "typeLiterals": "always"
+                }
+            }
+        ],
+        "variable-name": [true, "ban-keywords", "check-format", "allow-leading-underscore"]
+    }
+}

From 036a2b86d6929e92b05b950385b62fce31340ab5 Mon Sep 17 00:00:00 2001
From: David Chin <davidchin.yf@gmail.com>
Date: Thu, 18 Jan 2018 14:42:49 +1100
Subject: [PATCH 3/3] refactor(common): CHECKOUT-2507 Convert `DataStore`
 module into TypeScript

---
 package.json                                  |   2 +
 src/data-store/action.ts                      |   6 +
 src/data-store/action.typedef.js              |   7 -
 src/data-store/combine-reducers.ts            |  23 ++--
 src/data-store/compose-reducers.spec.ts       |   4 +-
 src/data-store/compose-reducers.ts            |  17 +--
 src/data-store/create-action.spec.ts          |   4 +-
 src/data-store/create-action.ts               |  21 ++-
 src/data-store/create-data-store.ts           |  18 +--
 src/data-store/create-error-action.spec.ts    |   4 +-
 src/data-store/create-error-action.ts         |  13 +-
 src/data-store/data-store.spec.ts             |  15 ++-
 src/data-store/data-store.ts                  | 122 ++++++++----------
 src/data-store/deep-freeze.spec.ts            |  19 ++-
 src/data-store/deep-freeze.ts                 |  24 ++--
 src/data-store/dispatchable-data-store.ts     |  14 ++
 .../dispatchable-data-store.typedef.js        |  12 --
 src/data-store/noop-action-transformer.ts     |  14 +-
 src/data-store/noop-state-transformer.ts      |  11 +-
 src/data-store/readable-data-store.ts         |  15 +++
 src/data-store/readable-data-store.typedef.js |  18 ---
 src/data-store/reducer.ts                     |   5 +
 src/data-store/reducer.typedef.js             |   6 -
 tsconfig.json                                 |   6 +
 yarn.lock                                     |  45 ++++++-
 25 files changed, 245 insertions(+), 200 deletions(-)
 create mode 100644 src/data-store/action.ts
 delete mode 100644 src/data-store/action.typedef.js
 create mode 100644 src/data-store/dispatchable-data-store.ts
 delete mode 100644 src/data-store/dispatchable-data-store.typedef.js
 create mode 100644 src/data-store/readable-data-store.ts
 delete mode 100644 src/data-store/readable-data-store.typedef.js
 create mode 100644 src/data-store/reducer.ts
 delete mode 100644 src/data-store/reducer.typedef.js

diff --git a/package.json b/package.json
index cd36d632ed..22afd1649c 100644
--- a/package.json
+++ b/package.json
@@ -46,6 +46,8 @@
   },
   "dependencies": {
     "@bigcommerce/request-sender": "git+ssh://git@github.com/bigcommerce/request-sender-js.git#0.1.0",
+    "@types/jest": "^21.1.10",
+    "@types/lodash": "^4.14.92",
     "bigpay-client": "git+ssh://git@github.com/bigcommerce-labs/bigpay-client-js.git#2.9.1",
     "form-poster": "git+ssh://git@github.com/bigcommerce-labs/form-poster-js.git#1.1.1",
     "lodash": "^4.17.4",
diff --git a/src/data-store/action.ts b/src/data-store/action.ts
new file mode 100644
index 0000000000..3e4abf9632
--- /dev/null
+++ b/src/data-store/action.ts
@@ -0,0 +1,6 @@
+export default interface Action<TPayload = any, TMeta = any> {
+    type: string;
+    error?: boolean;
+    meta?: TMeta;
+    payload?: TPayload;
+}
diff --git a/src/data-store/action.typedef.js b/src/data-store/action.typedef.js
deleted file mode 100644
index 21fb0e80f8..0000000000
--- a/src/data-store/action.typedef.js
+++ /dev/null
@@ -1,7 +0,0 @@
-/**
- * @typedef {Object} Action
- * @property {string} type
- * @property {Object} payload
- * @property {Object} meta
- * @property {?boolean} error
- */
diff --git a/src/data-store/combine-reducers.ts b/src/data-store/combine-reducers.ts
index 692fe73189..a708acdcea 100644
--- a/src/data-store/combine-reducers.ts
+++ b/src/data-store/combine-reducers.ts
@@ -1,18 +1,23 @@
-/**
- * @param {Object<string, Reducer>} reducers
- * @return {Reducer}
- */
-export default function combineReducers(reducers) {
+import Action from './action';
+import Reducer from './reducer';
+
+export default function combineReducers<TState, TAction extends Action>(
+    reducers: ReducerMap<TState, TAction>
+): Reducer<TState, TAction> {
     return (state, action) =>
-        Object.keys(reducers).reduce((result, key) => {
-            const reducer = reducers[key];
-            const currentState = state ? state[key] : undefined;
+        Object.keys(reducers).reduce((result: TState, key) => {
+            const reducer = reducers[key as keyof TState];
+            const currentState = state ? state[key as keyof TState] : undefined;
             const newState = reducer(currentState, action);
 
             if (currentState === newState && result) {
                 return result;
             }
 
-            return { ...result, [key]: newState };
+            return Object.assign({}, result, { [key]: newState });
         }, state);
 }
+
+export type ReducerMap<TState, TAction extends Action> = {
+    [Key in keyof TState]: Reducer<TState[Key], TAction>;
+};
diff --git a/src/data-store/compose-reducers.spec.ts b/src/data-store/compose-reducers.spec.ts
index fbbe085d31..a908a6143c 100644
--- a/src/data-store/compose-reducers.spec.ts
+++ b/src/data-store/compose-reducers.spec.ts
@@ -1,7 +1,7 @@
 import composeReducers from './compose-reducers';
 
 describe('composeReducers()', () => {
-    const fooReducer = (state, action) => {
+    const fooReducer = (state = '', action) => {
         switch (action.type) {
         case 'FOO':
             return 'foo';
@@ -14,7 +14,7 @@ describe('composeReducers()', () => {
         }
     };
 
-    const barReducer = (state, action) => {
+    const barReducer = (state = '', action) => {
         switch (action.type) {
         case 'BAR':
             return 'bar';
diff --git a/src/data-store/compose-reducers.ts b/src/data-store/compose-reducers.ts
index d5d1c6a144..1c717edcac 100644
--- a/src/data-store/compose-reducers.ts
+++ b/src/data-store/compose-reducers.ts
@@ -1,12 +1,13 @@
 import { curryRight, flowRight } from 'lodash';
+import Action from './action';
+import Reducer from './reducer';
 
-/**
- * @param {...Reducer} reducers
- * @return {Reducer}
- */
-export default function composeReducers(...reducers) {
+export default function composeReducers<TState, TAction extends Action>(
+    ...reducers: Array<Reducer<Partial<TState>, TAction>>
+): Reducer<TState, TAction> {
     return (state, action) =>
-        flowRight(...reducers.map(reducer =>
-            curryRight(reducer)(action)
-        ))(state);
+        flowRight.apply(
+            null,
+            reducers.map(reducer => curryRight(reducer)(action))
+        )(state);
 }
diff --git a/src/data-store/create-action.spec.ts b/src/data-store/create-action.spec.ts
index e16d2ad017..0a9c726481 100644
--- a/src/data-store/create-action.spec.ts
+++ b/src/data-store/create-action.spec.ts
@@ -15,7 +15,7 @@ describe('createAction()', () => {
         expect(action).toEqual({ type: 'ACTION' });
     });
 
-    it('throws an error if `type` is not provided', () => {
-        expect(() => createAction()).toThrow();
+    it('throws an error if `type` is not provided or empty', () => {
+        expect(() => createAction('')).toThrow();
     });
 });
diff --git a/src/data-store/create-action.ts b/src/data-store/create-action.ts
index d9f5fe9bd9..a82793564e 100644
--- a/src/data-store/create-action.ts
+++ b/src/data-store/create-action.ts
@@ -1,19 +1,14 @@
 import { omitBy } from 'lodash';
+import Action from './action';
 
-/**
- * @param {string} type
- * @param {Object} [payload]
- * @param {Object} [meta]
- * @return {Action}
- */
-export default function createAction(type, payload, meta) {
-    if (typeof type !== 'string') {
+export default function createAction<TPayload, TMeta>(
+    type: string,
+    payload?: TPayload,
+    meta?: TMeta
+): Action<TPayload, TMeta> {
+    if (typeof type !== 'string' || type === '') {
         throw new Error('`type` must be a string');
     }
 
-    return omitBy({
-        type,
-        payload,
-        meta,
-    }, value => value === undefined);
+    return { type, ...omitBy({ payload, meta }, value => value === undefined) };
 }
diff --git a/src/data-store/create-data-store.ts b/src/data-store/create-data-store.ts
index 8e65715a21..6d16d73f5a 100644
--- a/src/data-store/create-data-store.ts
+++ b/src/data-store/create-data-store.ts
@@ -1,13 +1,13 @@
-import combineReducers from './combine-reducers';
-import DataStore from './data-store';
+import Action from './action';
+import combineReducers, { ReducerMap } from './combine-reducers';
+import DataStore, { DataStoreOptions } from './data-store';
+import Reducer from './reducer';
 
-/**
- * @param {Reducer|Object<string, Reducer>} reducer
- * @param {Object} [initialState]
- * @param {Object} [options]
- * @return {DataStore}
- */
-export default function createDataStore(reducer, initialState, options) {
+export default function createDataStore<TState, TAction extends Action, TTransformedState = TState>(
+    reducer: Reducer<Partial<TState>, TAction> | ReducerMap<Partial<TState>, TAction>,
+    initialState: Partial<TState>,
+    options: DataStoreOptions<TState, TAction, TTransformedState>
+): DataStore<TState, TAction, TTransformedState> {
     if (typeof reducer === 'function') {
         return new DataStore(reducer, initialState, options);
     }
diff --git a/src/data-store/create-error-action.spec.ts b/src/data-store/create-error-action.spec.ts
index 7ac20ef412..c9515b51aa 100644
--- a/src/data-store/create-error-action.spec.ts
+++ b/src/data-store/create-error-action.spec.ts
@@ -15,7 +15,7 @@ describe('createErrorAction()', () => {
         expect(action).toEqual({ type: 'ACTION', error: true });
     });
 
-    it('throws an error if `type` is not provided', () => {
-        expect(() => createErrorAction()).toThrow();
+    it('throws an error if `type` is not provided or empty', () => {
+        expect(() => createErrorAction('')).toThrow();
     });
 });
diff --git a/src/data-store/create-error-action.ts b/src/data-store/create-error-action.ts
index 8c01bcafbf..3f65b366d6 100644
--- a/src/data-store/create-error-action.ts
+++ b/src/data-store/create-error-action.ts
@@ -1,12 +1,11 @@
+import Action from './action';
 import createAction from './create-action';
 
-/**
- * @param {string} type
- * @param {Object} [payload]
- * @param {Object} [meta]
- * @return {Action}
- */
-export default function createErrorAction(type, payload, meta) {
+export default function createErrorAction<TPayload, TMeta>(
+    type: string,
+    payload?: TPayload,
+    meta?: TMeta
+): Action<TPayload, TMeta> {
     return {
         ...createAction(type, payload, meta),
         error: true,
diff --git a/src/data-store/data-store.spec.ts b/src/data-store/data-store.spec.ts
index f6b3249422..37e68c7311 100644
--- a/src/data-store/data-store.spec.ts
+++ b/src/data-store/data-store.spec.ts
@@ -1,4 +1,5 @@
 import { Observable } from 'rxjs';
+import Action from './action';
 import DataStore from './data-store';
 
 describe('DataStore', () => {
@@ -31,7 +32,7 @@ describe('DataStore', () => {
 
         it('dispatches error actions and rejects with payload', async () => {
             const store = new DataStore(state => state);
-            const action = { error: true, payload: 'foobar' };
+            const action = { type: 'FOOBAR', error: true, payload: 'foobar' };
 
             try {
                 await store.dispatch(action);
@@ -52,7 +53,7 @@ describe('DataStore', () => {
             expect(await store.dispatch(Observable.of(
                 { type: 'APPEND', payload: 'foo' },
                 { type: 'APPEND', payload: 'bar' },
-                { type: 'APPEND', payload: '!!!' },
+                { type: 'APPEND', payload: '!!!' }
             ))).toEqual({ message: 'foobar!!!' });
         });
 
@@ -156,8 +157,8 @@ describe('DataStore', () => {
             const store = new DataStore(reducer);
 
             reducer.mockClear();
-            store.dispatch({});
-            store.dispatch({ payload: 'foobar' });
+            store.dispatch({ type: '' });
+            store.dispatch({ type: '', payload: 'foobar' });
 
             expect(reducer).not.toHaveBeenCalled();
         });
@@ -167,7 +168,7 @@ describe('DataStore', () => {
             const store = new DataStore(reducer);
 
             reducer.mockClear();
-            store.dispatch(Observable.of({}, { payload: 'foobar' }));
+            store.dispatch(Observable.of({ type: '', payload: 'foo' }, { type: '', payload: 'bar' }));
 
             expect(reducer).not.toHaveBeenCalled();
         });
@@ -290,7 +291,7 @@ describe('DataStore', () => {
                 default:
                     return state;
                 }
-            });
+            }, { foo: '', bar: '' });
             const subscriber = jest.fn();
 
             store.subscribe(subscriber, (state) => state.foo);
@@ -323,7 +324,7 @@ describe('DataStore', () => {
                 default:
                     return state;
                 }
-            });
+            }, { foo: '', bar: '', foobar: '' });
             const subscriber = jest.fn();
 
             store.subscribe(
diff --git a/src/data-store/data-store.ts b/src/data-store/data-store.ts
index 6cf2aaf582..7f2f25d4e3 100644
--- a/src/data-store/data-store.ts
+++ b/src/data-store/data-store.ts
@@ -2,9 +2,13 @@ import { isEqual } from 'lodash';
 import { BehaviorSubject } from 'rxjs/BehaviorSubject';
 import { Observable } from 'rxjs/Observable';
 import { Subject } from 'rxjs/Subject';
+import Action from './action';
 import deepFreeze from './deep-freeze';
+import DispatchableDataStore, { DispatchOptions } from './dispatchable-data-store';
 import noopActionTransformer from './noop-action-transformer';
 import noopStateTransformer from './noop-state-transformer';
+import ReadableDataStore, { Filter, Subscriber, Unsubscriber } from './readable-data-store';
+import Reducer from './reducer';
 import 'rxjs/add/observable/merge';
 import 'rxjs/add/observable/of';
 import 'rxjs/add/observable/throw';
@@ -17,52 +21,45 @@ import 'rxjs/add/operator/map';
 import 'rxjs/add/operator/mergeMap';
 import 'rxjs/add/operator/scan';
 
-/**
- * @implements {ReadableDataStore}
- * @implements {DispatchableDataStore}
- */
-export default class DataStore {
-    /**
-     * @param {Reducer} reducer
-     * @param {State} [initialState={}]
-     * @param {Object} [options={}]
-     * @param {boolean} [options.shouldWarnMutation=true]
-     * @param {function(state: State): TransformedState} [options.stateTransformer=noopStateTransformer]
-     * @param {function(action: Observable<Action<T>>): Observable<Action<T>>} [options.actionTransformer=noopActionTransformer]
-     * @return {void}
-     * @template State, TransformedState
-     */
-    constructor(reducer, initialState = {}, options = {}) {
+export default class DataStore<TState, TAction extends Action, TTransformedState = TState> implements ReadableDataStore<TTransformedState>, DispatchableDataStore<TTransformedState, TAction> {
+    private _options: DataStoreOptions<TState, TAction, TTransformedState>;
+    private _notification$: Subject<TTransformedState>;
+    private _dispatchers: { [key: string]: Dispatcher<TAction> };
+    private _dispatchQueue$: Subject<Dispatcher<TAction>>;
+    private _state$: BehaviorSubject<TTransformedState>;
+
+    constructor(
+        reducer: Reducer<Partial<TState>, TAction>,
+        initialState: Partial<TState> = {},
+        options?: DataStoreOptions<TState, TAction, TTransformedState>
+    ) {
         this._options = {
             shouldWarnMutation: true,
             stateTransformer: noopStateTransformer,
             actionTransformer: noopActionTransformer,
             ...options,
         };
-        this._state$ = new BehaviorSubject(initialState);
+        this._state$ = new BehaviorSubject(this._options.stateTransformer(initialState));
         this._notification$ = new Subject();
         this._dispatchers = {};
-        this._dispatchQueue$ = new Subject()
-            .mergeMap((dispatcher$) => dispatcher$.concatMap((action$) => action$))
-            .filter((action) => action.type);
+        this._dispatchQueue$ = new Subject();
 
         this._dispatchQueue$
+            .mergeMap((dispatcher$) => dispatcher$.concatMap((action$) => action$))
+            .filter((action) => !!action.type)
             .scan((state, action) => reducer(state, action), initialState)
             .distinctUntilChanged(isEqual)
             .map((state) => this._options.shouldWarnMutation === false ? state : deepFreeze(state))
             .map((state) => this._options.stateTransformer(state))
             .subscribe(this._state$);
 
-        this.dispatch({ type: 'INIT' });
+        this.dispatch({ type: 'INIT' } as TAction);
     }
 
-    /**
-     * @param {Action<T>|Observable<Action<T>>} action
-     * @param {Object} [options]
-     * @return {Promise<TransformedState>}
-     * @template T
-     */
-    dispatch(action, options) {
+    dispatch<TDispatchAction extends TAction>(
+        action: TDispatchAction | Observable<TDispatchAction>,
+        options?: DispatchOptions
+    ): Promise<TTransformedState> {
         if (action instanceof Observable) {
             return this._dispatchObservableAction(action, options);
         }
@@ -70,27 +67,19 @@ export default class DataStore {
         return this._dispatchAction(action);
     }
 
-    /**
-     * @return {TransformedState}
-     */
-    getState() {
+    getState(): TTransformedState {
         return this._state$.getValue();
     }
 
-    /**
-     * @return {void}
-     */
-    notifyState() {
+    notifyState(): void {
         this._notification$.next(this.getState());
     }
 
-    /**
-     * @param {function(state: TransformedState): void} subscriber
-     * @param {...function(state: TransformedState): any} [filters]
-     * @return {function(): void}
-     */
-    subscribe(subscriber, ...filters) {
-        let state$ = this._state$;
+    subscribe(
+        subscriber: Subscriber<TTransformedState>,
+        ...filters: Array<Filter<TTransformedState>>
+    ): Unsubscriber {
+        let state$: Observable<any> = this._state$;
 
         if (filters.length > 0) {
             state$ = state$.distinctUntilChanged((stateA, stateB) =>
@@ -106,27 +95,23 @@ export default class DataStore {
         return () => subscriptions.forEach((subscription) => subscription.unsubscribe());
     }
 
-    /**
-     * @private
-     * @param {Action<T>} action
-     * @return {Promise<TransformedState>}
-     * @template T
-     */
-    _dispatchAction(action) {
-        return this._dispatchObservableAction(action.error ? Observable.throw(action) : Observable.of(action));
+    private _dispatchAction<TDispatchAction extends TAction>(
+        action: TDispatchAction
+    ): Promise<TTransformedState> {
+        return this._dispatchObservableAction(
+            action.error ?
+                Observable.throw(action) :
+                Observable.of(action)
+        );
     }
 
-    /**
-     * @private
-     * @param {Observable<Action<T>>} action$
-     * @param {Object} [options]
-     * @return {Promise<TransformedState>}
-     * @template T
-     */
-    _dispatchObservableAction(action$, options = {}) {
+    private _dispatchObservableAction<TDispatchAction extends TAction>(
+        action$: Observable<TDispatchAction>,
+        options: DispatchOptions = {}
+    ): Promise<TTransformedState> {
         return new Promise((resolve, reject) => {
-            let action;
-            let error;
+            let action: TDispatchAction;
+            let error: any;
 
             this._getDispatcher(options.queueId).next(
                 this._options.actionTransformer(action$)
@@ -153,12 +138,7 @@ export default class DataStore {
         });
     }
 
-    /**
-     * @private
-     * @param {string} [queueId='default']
-     * @return {Subject<Action<T>>}
-     */
-    _getDispatcher(queueId = 'default') {
+    private _getDispatcher(queueId: string = 'default'): Dispatcher<TAction> {
         if (!this._dispatchers[queueId]) {
             this._dispatchers[queueId] = new Subject();
 
@@ -168,3 +148,11 @@ export default class DataStore {
         return this._dispatchers[queueId];
     }
 }
+
+export interface DataStoreOptions<TState, TAction, TTransformedState> {
+    shouldWarnMutation?: boolean;
+    actionTransformer?: (action: Observable<TAction>) => Observable<TAction>;
+    stateTransformer?: (state: Partial<TState>) => TTransformedState;
+}
+
+type Dispatcher<TAction> = Subject<Observable<TAction>>;
diff --git a/src/data-store/deep-freeze.spec.ts b/src/data-store/deep-freeze.spec.ts
index 0a28f7dc09..197561fe6e 100644
--- a/src/data-store/deep-freeze.spec.ts
+++ b/src/data-store/deep-freeze.spec.ts
@@ -2,7 +2,8 @@ import deepFreeze from './deep-freeze';
 
 describe('deepFreeze()', () => {
     it('throws error if mutating object', () => {
-        const object = deepFreeze({ message: 'Foobar' });
+        // Cast as `any` to bypass `Readonly` constraint.
+        const object = deepFreeze({ message: 'Foobar' }) as any;
 
         expect(() => { object.message = 'Hello'; }).toThrow();
         expect(() => { object.newMessage = 'Hello'; }).toThrow();
@@ -16,7 +17,8 @@ describe('deepFreeze()', () => {
     });
 
     it('throws error if mutating array', () => {
-        const array = deepFreeze(['Foobar']);
+        // Cast as `any` to bypass `ReadonlyArray` constraint.
+        const array = deepFreeze(['Foobar']) as any;
 
         expect(() => { array[0] = 'Hello'; }).toThrow();
         expect(() => { array.push('Hello'); }).toThrow();
@@ -36,4 +38,17 @@ describe('deepFreeze()', () => {
         expect(() => { object.child.message = 'Hello'; }).toThrow();
         expect(() => { collection[0].message = 'Hello'; }).toThrow();
     });
+
+    it('does not freeze primitive values', () => {
+        const value = 'Foobar';
+
+        expect(deepFreeze(value)).toBe(value);
+    });
+
+    it('does not freeze complex types', () => {
+        class Foobar {}
+        const object = new Foobar();
+
+        expect(deepFreeze(object)).toBe(object);
+    });
 });
diff --git a/src/data-store/deep-freeze.ts b/src/data-store/deep-freeze.ts
index 92a43a6250..c5527e18ac 100644
--- a/src/data-store/deep-freeze.ts
+++ b/src/data-store/deep-freeze.ts
@@ -1,20 +1,20 @@
 import { isPlainObject } from 'lodash';
 
-/**
- * @param {any} object
- * @return {any}
- */
-export default function deepFreeze(object) {
+export default function deepFreeze<T>(object: T[]): ReadonlyArray<T>;
+export default function deepFreeze<T extends object>(object: T): Readonly<T>;
+export default function deepFreeze<T>(object: T): T;
+export default function deepFreeze<T>(object: T[] | T): ReadonlyArray<T> | Readonly<T> | T {
     if (Object.isFrozen(object) || (!Array.isArray(object) && !isPlainObject(object))) {
         return object;
     }
 
-    return Object.freeze(
-        Object.getOwnPropertyNames(object)
-            .reduce((result, key) => {
-                result[key] = deepFreeze(object[key]);
+    if (Array.isArray(object)) {
+        return Object.freeze(object.map((value) => deepFreeze(value)));
+    }
+
+    return Object.freeze(Object.getOwnPropertyNames(object).reduce((result, key) => {
+        result[key as keyof T] = deepFreeze(object[key as keyof T]);
 
-                return result;
-            }, Array.isArray(object) ? [] : {})
-    );
+        return result;
+    }, {} as T));
 }
diff --git a/src/data-store/dispatchable-data-store.ts b/src/data-store/dispatchable-data-store.ts
new file mode 100644
index 0000000000..31239f5131
--- /dev/null
+++ b/src/data-store/dispatchable-data-store.ts
@@ -0,0 +1,14 @@
+import { Observable } from 'rxjs/Observable';
+import Action from './action';
+import ReadableDataStore from './readable-data-store';
+
+export default interface DispatchableDataStore<TTransformedState, TAction extends Action> extends ReadableDataStore<TTransformedState> {
+    dispatch: <TDispatchAction extends TAction>(
+        action: TDispatchAction | Observable<TDispatchAction>,
+        options?: DispatchOptions
+    ) => Promise<TTransformedState>;
+}
+
+export interface DispatchOptions {
+    queueId?: string;
+}
diff --git a/src/data-store/dispatchable-data-store.typedef.js b/src/data-store/dispatchable-data-store.typedef.js
deleted file mode 100644
index 9ad4c92697..0000000000
--- a/src/data-store/dispatchable-data-store.typedef.js
+++ /dev/null
@@ -1,12 +0,0 @@
-/**
- * @interface DispatchableDataStore
- * @template TransformedState
- */
-
-/**
- * @function
- * @name DispatchableDataStore#dispatch
- * @param {Action<T>} action
- * @return {Promise<TransformedState>}
- * @template T
- */
diff --git a/src/data-store/noop-action-transformer.ts b/src/data-store/noop-action-transformer.ts
index c2605a68ff..aae2be4017 100644
--- a/src/data-store/noop-action-transformer.ts
+++ b/src/data-store/noop-action-transformer.ts
@@ -1,8 +1,8 @@
-/**
- * @param {Observable<Action<T>>} action
- * @return {Observable<Action<T>>}
- * @template T
- */
-export default function noopActionTransformer(action) {
-    return action;
+import { Observable } from 'rxjs/Observable';
+import Action from './action';
+
+export default function noopActionTransformer<TAction extends Action, TTransformedAction extends Action = TAction>(
+    action: Observable<TAction>
+): Observable<TTransformedAction> {
+    return action as any as Observable<TTransformedAction>;
 }
diff --git a/src/data-store/noop-state-transformer.ts b/src/data-store/noop-state-transformer.ts
index 1f1847f8fc..474e12f8aa 100644
--- a/src/data-store/noop-state-transformer.ts
+++ b/src/data-store/noop-state-transformer.ts
@@ -1,8 +1,5 @@
-/**
- * @param {T} state
- * @return {T}
- * @template T
- */
-export default function noopStateTransformer(state) {
-    return state;
+export default function noopStateTransformer<TState, TTransformedState = TState>(
+    state: TState
+): TTransformedState {
+    return state as any as TTransformedState;
 }
diff --git a/src/data-store/readable-data-store.ts b/src/data-store/readable-data-store.ts
new file mode 100644
index 0000000000..16d585332f
--- /dev/null
+++ b/src/data-store/readable-data-store.ts
@@ -0,0 +1,15 @@
+import Action from './action';
+
+export default interface ReadableDataStore<TTransformedState> {
+    getState(): TTransformedState;
+    subscribe(
+        subscriber: Subscriber<TTransformedState>,
+        ...filters: Array<Filter<TTransformedState>>
+    ): Unsubscriber;
+}
+
+export type Filter<TState> = (state: TState) => any;
+
+export type Subscriber<TState> = (state: TState) => void;
+
+export type Unsubscriber = () => void;
diff --git a/src/data-store/readable-data-store.typedef.js b/src/data-store/readable-data-store.typedef.js
deleted file mode 100644
index 072523f29b..0000000000
--- a/src/data-store/readable-data-store.typedef.js
+++ /dev/null
@@ -1,18 +0,0 @@
-/**
- * @interface ReadableDataStore
- * @template TransformedState
- */
-
-/**
- * @function
- * @name ReadableDataStore#getState
- * @returns {TransformedState}
- */
-
-/**
- * @function
- * @name ReadableDataStore#subscribe
- * @param {function(state: TransformedState): void} subscriber
- * @param {...function(state: TransformedState): any} [filters]
- * @return {function(): void}
- */
diff --git a/src/data-store/reducer.ts b/src/data-store/reducer.ts
new file mode 100644
index 0000000000..36f6cfb418
--- /dev/null
+++ b/src/data-store/reducer.ts
@@ -0,0 +1,5 @@
+import Action from './action';
+
+type Reducer<TState, TAction extends Action> = (state: TState, action: TAction) => TState;
+
+export default Reducer;
diff --git a/src/data-store/reducer.typedef.js b/src/data-store/reducer.typedef.js
deleted file mode 100644
index 1c260ef0b1..0000000000
--- a/src/data-store/reducer.typedef.js
+++ /dev/null
@@ -1,6 +0,0 @@
-/**
- * @callback Reducer
- * @param {T} state
- * @param {Action} action
- * @returns {T}
- */
diff --git a/tsconfig.json b/tsconfig.json
index 96a1c1d240..135cb9a78b 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,6 +5,12 @@
         "experimentalDecorators": true,
         "forceConsistentCasingInFileNames": true,
         "importHelpers": true,
+        "lib": [
+            "dom",
+            "dom.iterable",
+            "es6",
+            "scripthost",
+        ],
         "moduleResolution": "node",
         "removeComments": true,
         "skipLibCheck": true,
diff --git a/yarn.lock b/yarn.lock
index e5b4cab0af..807ba00b50 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -11,6 +11,14 @@
     query-string "^5.0.0"
     tslib "^1.8.0"
 
+"@types/jest@^21.1.10":
+  version "21.1.10"
+  resolved "https://registry.yarnpkg.com/@types/jest/-/jest-21.1.10.tgz#dcacb5217ddf997a090cc822bba219b4b2fd7984"
+
+"@types/lodash@^4.14.92":
+  version "4.14.92"
+  resolved "https://registry.yarnpkg.com/@types/lodash/-/lodash-4.14.92.tgz#6e3cb0b71a1e12180a47a42a744e856c3ae99a57"
+
 JSONStream@^1.0.4:
   version "1.3.1"
   resolved "https://registry.yarnpkg.com/JSONStream/-/JSONStream-1.3.1.tgz#707f761e01dae9e16f1bcf93703b78c70966579a"
@@ -294,7 +302,7 @@ aws4@^1.2.1, aws4@^1.6.0:
   version "1.6.0"
   resolved "https://registry.yarnpkg.com/aws4/-/aws4-1.6.0.tgz#83ef5ca860b2b32e4a0deedee8c771b9db57471e"
 
-babel-code-frame@^6.26.0:
+babel-code-frame@^6.22.0, babel-code-frame@^6.26.0:
   version "6.26.0"
   resolved "https://registry.yarnpkg.com/babel-code-frame/-/babel-code-frame-6.26.0.tgz#63fd43f7dc1e3bb7ce35947db8fe369a3f58c74b"
   dependencies:
@@ -626,7 +634,7 @@ buffer@^4.3.0:
     ieee754 "^1.1.4"
     isarray "^1.0.0"
 
-builtin-modules@^1.0.0:
+builtin-modules@^1.0.0, builtin-modules@^1.1.1:
   version "1.1.1"
   resolved "https://registry.yarnpkg.com/builtin-modules/-/builtin-modules-1.1.1.tgz#270f076c5a72c02f5b65a47df94c5fe3a278892f"
 
@@ -806,6 +814,10 @@ combined-stream@^1.0.5, combined-stream@~1.0.5:
   dependencies:
     delayed-stream "~1.0.0"
 
+commander@^2.12.1:
+  version "2.13.0"
+  resolved "https://registry.yarnpkg.com/commander/-/commander-2.13.0.tgz#6964bca67685df7c1f1430c584f07d7597885b9c"
+
 commander@^2.9.0, commander@~2.12.1:
   version "2.12.2"
   resolved "https://registry.yarnpkg.com/commander/-/commander-2.12.2.tgz#0f5946c427ed9ec0d91a46bb9def53e54650e555"
@@ -3839,7 +3851,7 @@ resolve@1.1.7:
   version "1.1.7"
   resolved "https://registry.yarnpkg.com/resolve/-/resolve-1.1.7.tgz#203114d82ad2c5ed9e8e0411b3932875e889e97b"
 
-resolve@^1.1.7:
+resolve@^1.1.7, resolve@^1.3.2:
   version "1.5.0"
   resolved "https://registry.yarnpkg.com/resolve/-/resolve-1.5.0.tgz#1f09acce796c9a762579f31b2c1cc4c3cddf9f36"
   dependencies:
@@ -4438,6 +4450,33 @@ tslib@^1.8.0:
   version "1.8.0"
   resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.8.0.tgz#dc604ebad64bcbf696d613da6c954aa0e7ea1eb6"
 
+tslib@^1.8.1:
+  version "1.8.1"
+  resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.8.1.tgz#6946af2d1d651a7b1863b531d6e5afa41aa44eac"
+
+tslint@^5.9.1:
+  version "5.9.1"
+  resolved "https://registry.yarnpkg.com/tslint/-/tslint-5.9.1.tgz#1255f87a3ff57eb0b0e1f0e610a8b4748046c9ae"
+  dependencies:
+    babel-code-frame "^6.22.0"
+    builtin-modules "^1.1.1"
+    chalk "^2.3.0"
+    commander "^2.12.1"
+    diff "^3.2.0"
+    glob "^7.1.1"
+    js-yaml "^3.7.0"
+    minimatch "^3.0.4"
+    resolve "^1.3.2"
+    semver "^5.3.0"
+    tslib "^1.8.0"
+    tsutils "^2.12.1"
+
+tsutils@^2.12.1:
+  version "2.19.0"
+  resolved "https://registry.yarnpkg.com/tsutils/-/tsutils-2.19.0.tgz#170a267c1df5ae046e902568ca3444a1a4dfcb3a"
+  dependencies:
+    tslib "^1.8.1"
+
 tty-browserify@0.0.0:
   version "0.0.0"
   resolved "https://registry.yarnpkg.com/tty-browserify/-/tty-browserify-0.0.0.tgz#a157ba402da24e9bf957f9aa69d524eed42901a6"