diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4c3499115..f310bdf84 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -25,10 +25,10 @@ jobs:
       - run: npm ci
       - name: Build Types
         run: npm run build:types
-      - name: Lint Types
-        run: npm run lint:types
       - name: Test Types
         run: npm run test:types
+      - name: Lint Types
+        run: npm run lint:types
   check-docs:
     name: Check Docs
     timeout-minutes: 5
diff --git a/src/CoreManager.ts b/src/CoreManager.ts
index 9ee9697ba..dff47e32a 100644
--- a/src/CoreManager.ts
+++ b/src/CoreManager.ts
@@ -15,9 +15,6 @@ import type ParseConfig from './ParseConfig';
 import type LiveQueryClient from './LiveQueryClient';
 import type ParseSchema from './ParseSchema';
 import type ParseInstallation from './ParseInstallation';
-import type ParseQuery from './ParseQuery';
-import type * as ParseOp from './ParseOp';
-import type ParseRole from './ParseRole';
 
 type AnalyticsController = {
   track: (name: string, dimensions: { [key: string]: string }) => Promise<any>,
@@ -598,7 +595,7 @@ const CoreManager = {
     return config['HooksController']!;
   },
 
-  setParseOp(op: typeof ParseOp) {
+  setParseOp(op: any) {
     config['ParseOp'] = op;
   },
 
@@ -606,35 +603,35 @@ const CoreManager = {
     return config['ParseOp']!;
   },
 
-  setParseObject(object: typeof ParseObject) {
+  setParseObject(object: any) {
     config['ParseObject'] = object;
   },
 
-  getParseObject(): ParseObject {
+  getParseObject() {
     return config['ParseObject']!;
   },
 
-  setParseQuery(query: typeof ParseQuery) {
+  setParseQuery(query: any) {
     config['ParseQuery'] = query;
   },
 
-  getParseQuery(): ParseQuery {
+  getParseQuery() {
     return config['ParseQuery']!;
   },
 
-  setParseRole(role: typeof ParseRole) {
+  setParseRole(role: any) {
     config['ParseRole'] = role;
   },
 
-  getParseRole(): ParseRole {
+  getParseRole() {
     return config['ParseRole']!;
   },
 
-  setParseUser(user: typeof ParseUser) {
+  setParseUser(user: any) {
     config['ParseUser'] = user;
   },
 
-  getParseUser(): ParseUser {
+  getParseUser() {
     return config['ParseUser']!;
   },
 };
diff --git a/src/ParseObject.ts b/src/ParseObject.ts
index 23c699524..f00be9eef 100644
--- a/src/ParseObject.ts
+++ b/src/ParseObject.ts
@@ -2385,7 +2385,7 @@ const DefaultController = {
     return Promise.resolve(target);
   },
 
-  save(target: ParseObject | Array<ParseObject | ParseFile>, options: RequestOptions): Promise<ParseObject | Array<ParseObject> | ParseFile> {
+  save(target: ParseObject | null | Array<ParseObject | ParseFile>, options: RequestOptions): Promise<ParseObject | Array<ParseObject> | ParseFile> {
     const batchSize =
       options && options.batchSize ? options.batchSize : CoreManager.get('REQUEST_BATCH_SIZE');
     const localDatastore = CoreManager.getLocalDatastore();
@@ -2452,11 +2452,11 @@ const DefaultController = {
 
             // Queue up tasks for each object in the batch.
             // When every task is ready, the API request will execute
-            const batchReturned = new resolvingPromise();
-            const batchReady = [];
-            const batchTasks = [];
+            const batchReturned = resolvingPromise();
+            const batchReady: ReturnType<typeof resolvingPromise<void>>[] = [];
+            const batchTasks: Promise<void>[] = [];
             batch.forEach((obj, index) => {
-              const ready = new resolvingPromise();
+              const ready = resolvingPromise<void>();
               batchReady.push(ready);
               const task = function () {
                 ready.resolve();
diff --git a/src/__tests__/escape-test.js b/src/__tests__/escape-test.js
index 11e6e07af..767d5723a 100644
--- a/src/__tests__/escape-test.js
+++ b/src/__tests__/escape-test.js
@@ -1,6 +1,6 @@
 jest.autoMockOff();
 
-const escape = require('../escape.js').default;
+const escape = require('../escape').default;
 
 describe('escape', () => {
   it('escapes special HTML characters', () => {
diff --git a/src/arrayContainsObject.js b/src/arrayContainsObject.ts
similarity index 96%
rename from src/arrayContainsObject.js
rename to src/arrayContainsObject.ts
index 188d21cfa..3c4ba6188 100644
--- a/src/arrayContainsObject.js
+++ b/src/arrayContainsObject.ts
@@ -1,7 +1,3 @@
-/**
- * @flow
- */
-
 import CoreManager from './CoreManager';
 import type ParseObject from './ParseObject';
 
diff --git a/src/canBeSerialized.js b/src/canBeSerialized.ts
similarity index 98%
rename from src/canBeSerialized.js
rename to src/canBeSerialized.ts
index 3923a3545..a109b9236 100644
--- a/src/canBeSerialized.js
+++ b/src/canBeSerialized.ts
@@ -1,7 +1,3 @@
-/**
- * @flow
- */
-
 import CoreManager from './CoreManager';
 import ParseFile from './ParseFile';
 import type ParseObject from './ParseObject';
diff --git a/src/decode.js b/src/decode.ts
similarity index 94%
rename from src/decode.js
rename to src/decode.ts
index c358437a0..fc4c876ca 100644
--- a/src/decode.js
+++ b/src/decode.ts
@@ -1,8 +1,4 @@
-/**
- * @flow
- */
 import CoreManager from './CoreManager';
-import ParseACL from './ParseACL'; // eslint-disable-line no-unused-vars
 import ParseFile from './ParseFile';
 import ParseGeoPoint from './ParseGeoPoint';
 import ParsePolygon from './ParsePolygon';
diff --git a/src/encode.js b/src/encode.ts
similarity index 93%
rename from src/encode.js
rename to src/encode.ts
index 3bcba74f3..e5558400f 100644
--- a/src/encode.js
+++ b/src/encode.ts
@@ -1,7 +1,3 @@
-/**
- * @flow
- */
-
 import CoreManager from './CoreManager';
 import ParseACL from './ParseACL';
 import ParseFile from './ParseFile';
@@ -10,10 +6,10 @@ import ParsePolygon from './ParsePolygon';
 import ParseRelation from './ParseRelation';
 
 function encode(
-  value: mixed,
+  value: any,
   disallowObjects: boolean,
   forcePointers: boolean,
-  seen: Array<mixed>,
+  seen: Array<any>,
   offline: boolean
 ): any {
   const ParseObject = CoreManager.getParseObject();
@@ -57,7 +53,7 @@ function encode(
     if (isNaN(value)) {
       throw new Error('Tried to encode an invalid date.');
     }
-    return { __type: 'Date', iso: (value: any).toJSON() };
+    return { __type: 'Date', iso: (value as Date).toJSON() };
   }
   if (
     Object.prototype.toString.call(value) === '[object RegExp]' &&
@@ -84,10 +80,10 @@ function encode(
 }
 
 export default function (
-  value: mixed,
+  value: any,
   disallowObjects?: boolean,
   forcePointers?: boolean,
-  seen?: Array<mixed>,
+  seen?: Array<any>,
   offline?: boolean
 ): any {
   return encode(value, !!disallowObjects, !!forcePointers, seen || [], offline);
diff --git a/src/equals.js b/src/equals.ts
similarity index 96%
rename from src/equals.js
rename to src/equals.ts
index bbc731f04..08b4d42da 100644
--- a/src/equals.js
+++ b/src/equals.ts
@@ -3,7 +3,7 @@ import ParseACL from './ParseACL';
 import ParseFile from './ParseFile';
 import ParseGeoPoint from './ParseGeoPoint';
 
-export default function equals(a, b) {
+export default function equals(a: any, b: any): boolean {
   const toString = Object.prototype.toString;
   if (toString.call(a) === '[object Date]' || toString.call(b) === '[object Date]') {
     const dateA = new Date(a);
diff --git a/src/escape.js b/src/escape.ts
similarity index 93%
rename from src/escape.js
rename to src/escape.ts
index e4b101aee..e7e6308e7 100644
--- a/src/escape.js
+++ b/src/escape.ts
@@ -1,7 +1,3 @@
-/*
- * @flow
- */
-
 const encoded = {
   '&': '&amp;',
   '<': '&lt;',
diff --git a/src/isRevocableSession.js b/src/isRevocableSession.ts
similarity index 85%
rename from src/isRevocableSession.js
rename to src/isRevocableSession.ts
index 5da2de5fb..75309509b 100644
--- a/src/isRevocableSession.js
+++ b/src/isRevocableSession.ts
@@ -1,7 +1,3 @@
-/**
- * @flow
- */
-
 export default function isRevocableSession(token: string): boolean {
   return token.indexOf('r:') > -1;
 }
diff --git a/src/parseDate.js b/src/parseDate.ts
similarity index 88%
rename from src/parseDate.js
rename to src/parseDate.ts
index 04ff6ea7f..13e922619 100644
--- a/src/parseDate.js
+++ b/src/parseDate.ts
@@ -1,8 +1,4 @@
-/**
- * @flow
- */
-
-export default function parseDate(iso8601: string): ?Date {
+export default function parseDate(iso8601: string): Date | null {
   const regexp = new RegExp(
     '^([0-9]{1,4})-([0-9]{1,2})-([0-9]{1,2})' +
       'T' +
diff --git a/src/promiseUtils.js b/src/promiseUtils.ts
similarity index 70%
rename from src/promiseUtils.js
rename to src/promiseUtils.ts
index 176c32a0b..8e82a8191 100644
--- a/src/promiseUtils.js
+++ b/src/promiseUtils.ts
@@ -1,17 +1,18 @@
 // Create Deferred Promise
-export function resolvingPromise() {
-  let res;
-  let rej;
-  const promise = new Promise((resolve, reject) => {
+export function resolvingPromise<T = any>() {
+  let res: (value: T) => void;
+  let rej: (error: T) => void;
+  const promise = new Promise<T>((resolve, reject) => {
     res = resolve;
     rej = reject;
   });
-  promise.resolve = res;
-  promise.reject = rej;
-  return promise;
+  const defer: typeof promise & { resolve: (res: T) => void, reject: (err: any) => void } = promise as any;
+  defer.resolve = res!;
+  defer.reject = rej!;
+  return defer;
 }
 
-export function when(promises) {
+export function when(promises: any) {
   let objects;
   const arrayArgument = Array.isArray(promises);
   if (arrayArgument) {
@@ -32,7 +33,7 @@ export function when(promises) {
     return Promise.resolve(returnValue);
   }
 
-  const promise = new resolvingPromise();
+  const promise = resolvingPromise();
 
   const resolveOne = function () {
     total--;
@@ -45,7 +46,7 @@ export function when(promises) {
     }
   };
 
-  const chain = function (object, index) {
+  const chain = function (object: Promise<any>, index: number) {
     if (object && typeof object.then === 'function') {
       object.then(
         function (result) {
@@ -70,7 +71,7 @@ export function when(promises) {
   return promise;
 }
 
-export function continueWhile(test, emitter) {
+export function continueWhile(test: () => any, emitter: () => Promise<any>) {
   if (test()) {
     return emitter().then(() => {
       return continueWhile(test, emitter);
diff --git a/src/unique.js b/src/unique.ts
similarity index 81%
rename from src/unique.js
rename to src/unique.ts
index 15bf6248b..fd31f74bf 100644
--- a/src/unique.js
+++ b/src/unique.ts
@@ -1,16 +1,12 @@
-/**
- * @flow
- */
-
 import arrayContainsObject from './arrayContainsObject';
 import CoreManager from './CoreManager';
 
 export default function unique<T>(arr: Array<T>): Array<T> {
-  const uniques = [];
+  const uniques: T[] = [];
   arr.forEach(value => {
     const ParseObject = CoreManager.getParseObject();
     if (value instanceof ParseObject) {
-      if (!arrayContainsObject(uniques, value)) {
+      if (!arrayContainsObject(uniques, value as typeof ParseObject)) {
         uniques.push(value);
       }
     } else {
diff --git a/src/unsavedChildren.js b/src/unsavedChildren.ts
similarity index 96%
rename from src/unsavedChildren.js
rename to src/unsavedChildren.ts
index 3386e91c8..ce11d2966 100644
--- a/src/unsavedChildren.js
+++ b/src/unsavedChildren.ts
@@ -1,7 +1,3 @@
-/**
- * @flow
- */
-
 import CoreManager from './CoreManager';
 import ParseFile from './ParseFile';
 import type ParseObject from './ParseObject';
@@ -69,7 +65,7 @@ function traverse(
     return;
   }
   if (obj instanceof ParseFile) {
-    if (!obj.url() && encountered.files.indexOf(obj) < 0) {
+    if (!(obj as ParseFile).url() && encountered.files.indexOf(obj) < 0) {
       encountered.files.push(obj);
     }
     return;
diff --git a/src/uuid.ts b/src/uuid.ts
index 03be8a07e..1ba54b844 100644
--- a/src/uuid.ts
+++ b/src/uuid.ts
@@ -1,6 +1,6 @@
 import { v4 } from 'uuid';
 
-let uuid: () => string = null as any;
+let uuid: () => string;
 
 if (process.env.PARSE_BUILD === 'weapp') {
   uuid = function () {
diff --git a/types/CoreManager.d.ts b/types/CoreManager.d.ts
index 3dde6b121..dcf8cfcf4 100644
--- a/types/CoreManager.d.ts
+++ b/types/CoreManager.d.ts
@@ -286,13 +286,13 @@ declare const CoreManager: {
     getHooksController(): HooksController;
     setParseOp(op: any): void;
     getParseOp(): any;
-    setParseObject(object: typeof ParseObject): void;
-    getParseObject(): ParseObject;
+    setParseObject(object: any): void;
+    getParseObject(): any;
     setParseQuery(query: any): void;
-    getParseQuery(): ParseQuery;
+    getParseQuery(): any;
     setParseRole(role: any): void;
-    getParseRole(): ParseRole;
+    getParseRole(): any;
     setParseUser(user: any): void;
-    getParseUser(): ParseUser;
+    getParseUser(): any;
 };
 export default CoreManager;
diff --git a/types/arrayContainsObject.d.ts b/types/arrayContainsObject.d.ts
index 764acda42..a6a357188 100644
--- a/types/arrayContainsObject.d.ts
+++ b/types/arrayContainsObject.d.ts
@@ -1,2 +1,2 @@
+import type ParseObject from './ParseObject';
 export default function arrayContainsObject(array: Array<any>, object: ParseObject): boolean;
-import ParseObject from './ParseObject';
diff --git a/types/canBeSerialized.d.ts b/types/canBeSerialized.d.ts
index 7cc2db046..fdf8e3775 100644
--- a/types/canBeSerialized.d.ts
+++ b/types/canBeSerialized.d.ts
@@ -1,2 +1,2 @@
+import type ParseObject from './ParseObject';
 export default function canBeSerialized(obj: ParseObject): boolean;
-import ParseObject from './ParseObject';
diff --git a/types/encode.d.ts b/types/encode.d.ts
index 510cff8d7..d63c1e75a 100644
--- a/types/encode.d.ts
+++ b/types/encode.d.ts
@@ -1 +1 @@
-export default function _default(value: mixed, disallowObjects?: boolean, forcePointers?: boolean, seen?: Array<mixed>, offline?: boolean): any;
+export default function (value: any, disallowObjects?: boolean, forcePointers?: boolean, seen?: Array<any>, offline?: boolean): any;
diff --git a/types/isRevocableSession.d.ts b/types/isRevocableSession.d.ts
index 29d483cbb..f85d82130 100644
--- a/types/isRevocableSession.d.ts
+++ b/types/isRevocableSession.d.ts
@@ -1,4 +1 @@
-/**
- * @flow
- */
 export default function isRevocableSession(token: string): boolean;
diff --git a/types/parseDate.d.ts b/types/parseDate.d.ts
index 4ec986b68..45630f59e 100644
--- a/types/parseDate.d.ts
+++ b/types/parseDate.d.ts
@@ -1,4 +1 @@
-/**
- * @flow
- */
 export default function parseDate(iso8601: string): Date | null;
diff --git a/types/promiseUtils.d.ts b/types/promiseUtils.d.ts
index ae6efac22..e652712a0 100644
--- a/types/promiseUtils.d.ts
+++ b/types/promiseUtils.d.ts
@@ -1,3 +1,9 @@
-export function resolvingPromise(): Promise<any>;
-export function when(promises: any, ...args: any[]): any;
-export function continueWhile(test: any, emitter: any): any;
+export declare function resolvingPromise<T = any>(): Promise<T> & {
+    resolve: (res: T) => void;
+    reject: (err: any) => void;
+};
+export declare function when(promises: any): Promise<any[]> | (Promise<any> & {
+    resolve: (res: any) => void;
+    reject: (err: any) => void;
+});
+export declare function continueWhile(test: () => any, emitter: () => Promise<any>): any;
diff --git a/types/unique.d.ts b/types/unique.d.ts
index 1736d2e04..c305608cf 100644
--- a/types/unique.d.ts
+++ b/types/unique.d.ts
@@ -1 +1 @@
-export default function unique<T>(arr: T[]): T[];
+export default function unique<T>(arr: Array<T>): Array<T>;
diff --git a/types/unsavedChildren.d.ts b/types/unsavedChildren.d.ts
index ec1be90ca..57881ba36 100644
--- a/types/unsavedChildren.d.ts
+++ b/types/unsavedChildren.d.ts
@@ -1,3 +1,5 @@
+import ParseFile from './ParseFile';
+import type ParseObject from './ParseObject';
 /**
  * Return an array of unsaved children, which are either Parse Objects or Files.
  * If it encounters any dirty Objects without Ids, it will throw an exception.
@@ -7,5 +9,3 @@
  * @returns {Array}
  */
 export default function unsavedChildren(obj: ParseObject, allowDeepUnsaved?: boolean): Array<ParseFile | ParseObject>;
-import ParseObject from './ParseObject';
-import ParseFile from './ParseFile';