diff --git a/js/constants.ts b/js/constants.ts
index fa784b72..fde799b4 100644
--- a/js/constants.ts
+++ b/js/constants.ts
@@ -1,4 +1,4 @@
-import { Band, MediaTagRequestStatus } from "./types";
+import { Band, MediaTagRequestStatus, MediaStatus } from "./types";
 import * as baseSkin from "./baseSkin.json";
 export const BANDS: Band[] = [
   60,
@@ -63,7 +63,8 @@ export const TIME_MODE = {
   REMAINING: "REMAINING"
 };
 
-export const MEDIA_STATUS = {
+// TODO: Convert to enum once we are fully Typescript
+export const MEDIA_STATUS: Record<MediaStatus, MediaStatus> = {
   PLAYING: "PLAYING",
   STOPPED: "STOPPED",
   PAUSED: "PAUSED"
diff --git a/js/media/elementSource.js b/js/media/elementSource.ts
similarity index 89%
rename from js/media/elementSource.js
rename to js/media/elementSource.ts
index 3796b380..701a2e30 100644
--- a/js/media/elementSource.js
+++ b/js/media/elementSource.ts
@@ -1,13 +1,22 @@
 import Emitter from "../emitter";
 import { clamp } from "../utils";
 import { MEDIA_STATUS } from "../constants";
+import { MediaStatus } from "../types";
 
 export default class ElementSource {
-  on(eventType, cb) {
+  _emitter: Emitter;
+  _context: AudioContext;
+  _source: AudioNode;
+  _destination: AudioNode;
+  _audio: HTMLAudioElement;
+  _stalled: boolean;
+  _status: MediaStatus;
+
+  on(eventType: string, cb: (...args: any[]) => void) {
     return this._emitter.on(eventType, cb);
   }
 
-  constructor(context, destination) {
+  constructor(context: AudioContext, destination: AudioNode) {
     this._emitter = new Emitter();
     this._context = context;
     this._destination = destination;
@@ -36,7 +45,7 @@ export default class ElementSource {
     });
 
     this._audio.addEventListener("error", e => {
-      switch (this._audio.error.code) {
+      switch (this._audio.error!.code) {
         case 1:
           // The fetching of the associated resource was aborted by the user's request.
           console.error("MEDIA_ERR_ABORTED", e);
@@ -69,7 +78,7 @@ export default class ElementSource {
     this._source.connect(destination);
   }
 
-  _setStalled(stalled) {
+  _setStalled(stalled: boolean) {
     this._stalled = stalled;
     this._emitter.trigger("stallChanged");
   }
@@ -80,7 +89,7 @@ export default class ElementSource {
 
   // Async for now, for compatibility with BufferAudioSource
   // TODO: This does not need to be async
-  async loadUrl(url) {
+  async loadUrl(url: string) {
     this._audio.src = url;
   }
 
@@ -107,7 +116,7 @@ export default class ElementSource {
     this._setStatus(MEDIA_STATUS.STOPPED);
   }
 
-  seekToTime(time) {
+  seekToTime(time: number) {
     /* TODO: We could check if this is actually seekable:
     const { seekable } = this._audio;
     for (let i = 0; i < seekable.length; i++) {
@@ -148,7 +157,7 @@ export default class ElementSource {
     return this._context.sampleRate;
   }
 
-  _setStatus(status) {
+  _setStatus(status: MediaStatus) {
     this._status = status;
     this._emitter.trigger("statusChange");
   }
diff --git a/js/types.ts b/js/types.ts
index e98f6d0d..e0523ca7 100644
--- a/js/types.ts
+++ b/js/types.ts
@@ -393,6 +393,8 @@ export type MediaTagRequestStatus =
   | "COMPLETE"
   | "NOT_REQUESTED";
 
+export type MediaStatus = "PLAYING" | "STOPPED" | "PAUSED";
+
 export interface PlaylistTrack {
   artist: string;
   title: string;
diff --git a/package.json b/package.json
index 94c0186c..527fd5bc 100644
--- a/package.json
+++ b/package.json
@@ -63,6 +63,7 @@
     "@types/react": "^16.4.14",
     "@types/react-dom": "^16.0.7",
     "@types/react-redux": "^6.0.8",
+    "@types/webaudioapi": "^0.0.27",
     "babel-core": "7.0.0-bridge.0",
     "babel-eslint": "^9.0.0-beta.3",
     "babel-jest": "^23.4.2",
diff --git a/yarn.lock b/yarn.lock
index 147f7bc1..aa14d29c 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -760,6 +760,10 @@
     "@types/prop-types" "*"
     csstype "^2.2.0"
 
+"@types/webaudioapi@^0.0.27":
+  version "0.0.27"
+  resolved "https://registry.yarnpkg.com/@types/webaudioapi/-/webaudioapi-0.0.27.tgz#8a3f98eaa07cb577be2dae22311d37c3b545f74f"
+
 abab@^1.0.4:
   version "1.0.4"
   resolved "https://registry.yarnpkg.com/abab/-/abab-1.0.4.tgz#5faad9c2c07f60dd76770f71cf025b62a63cfd4e"