diff --git a/src/addons/attach/attach.test.ts b/src/addons/attach/attach.test.ts
index 9bf0e070..a13885bb 100644
--- a/src/addons/attach/attach.test.ts
+++ b/src/addons/attach/attach.test.ts
@@ -5,7 +5,7 @@
 
 import { assert, expect } from 'chai';
 
-import * as attach from './attach'
+import * as attach from './attach';
 
 class MockTerminal {}
 
diff --git a/src/addons/attach/attach.ts b/src/addons/attach/attach.ts
index 4e0d5941..349a03dd 100644
--- a/src/addons/attach/attach.ts
+++ b/src/addons/attach/attach.ts
@@ -16,16 +16,16 @@
  *                             should happen instantly or at a maximum
  *                             frequency of 1 rendering per 10ms.
  */
-export function attach(term, socket, bidirectional, buffered) {
-  bidirectional = (typeof bidirectional == 'undefined') ? true : bidirectional;
+export function attach(term: any, socket: WebSocket, bidirectional: boolean, buffered: boolean): void {
+  bidirectional = (typeof bidirectional === 'undefined') ? true : bidirectional;
   term.socket = socket;
 
-  term._flushBuffer = function() {
+  term._flushBuffer = () => {
     term.write(term._attachSocketBuffer);
     term._attachSocketBuffer = null;
   };
 
-  term._pushToBuffer = function(data) {
+  term._pushToBuffer = (data: string) => {
     if (term._attachSocketBuffer) {
       term._attachSocketBuffer += data;
     } else {
@@ -34,20 +34,19 @@ export function attach(term, socket, bidirectional, buffered) {
     }
   };
 
-  var myTextDecoder;
+  let myTextDecoder;
 
-  term._getMessage = function(ev) {
-    var str;
-    if (typeof ev.data === "object") {
+  term._getMessage = function(ev: MessageEvent): void {
+    let str;
+    if (typeof ev.data === 'object') {
       if (ev.data instanceof ArrayBuffer) {
           if (!myTextDecoder) {
             myTextDecoder = new TextDecoder();
           }
 
           str = myTextDecoder.decode( ev.data );
-      }
-      else {
-        throw "TODO: handle Blob?";
+      } else {
+        throw 'TODO: handle Blob?';
       }
     }
 
@@ -58,7 +57,7 @@ export function attach(term, socket, bidirectional, buffered) {
     }
   };
 
-  term._sendData = function(data) {
+  term._sendData = (data: string) => {
     if (socket.readyState !== 1) {
       return;
     }
@@ -82,10 +81,10 @@ export function attach(term, socket, bidirectional, buffered) {
  * @param {WebSocket} socket - The socket from which to detach the current
  *                             terminal.
  */
-export function detach(term, socket) {
+export function detach(term: any, socket: WebSocket): void {
   term.off('data', term._sendData);
 
-  socket = (typeof socket == 'undefined') ? term.socket : socket;
+  socket = (typeof socket === 'undefined') ? term.socket : socket;
 
   if (socket) {
     socket.removeEventListener('message', term._getMessage);
@@ -95,7 +94,7 @@ export function detach(term, socket) {
 };
 
 
-export function apply(terminalConstructor) {
+export function apply(terminalConstructor: any): void {
   /**
    * Attaches the current terminal to the given socket
    *
@@ -106,7 +105,7 @@ export function apply(terminalConstructor) {
    *                             should happen instantly or at a maximum
    *                             frequency of 1 rendering per 10ms.
    */
-  terminalConstructor.prototype.attach = function(socket, bidirectional, buffered) {
+  terminalConstructor.prototype.attach = (socket: WebSocket, bidirectional: boolean, buffered: boolean) => {
     return attach(this, socket, bidirectional, buffered);
   };
 
@@ -116,7 +115,7 @@ export function apply(terminalConstructor) {
    * @param {WebSocket} socket - The socket from which to detach the current
    *                             terminal.
    */
-  terminalConstructor.prototype.detach = function(socket) {
+  terminalConstructor.prototype.detach = (socket: WebSocket) => {
     return detach(this, socket);
   };
-}
+};
diff --git a/src/addons/fit/fit.test.ts b/src/addons/fit/fit.test.ts
index 159cc987..0dc17963 100644
--- a/src/addons/fit/fit.test.ts
+++ b/src/addons/fit/fit.test.ts
@@ -5,7 +5,7 @@
 
 import { assert, expect } from 'chai';
 
-import * as fit from './fit'
+import * as fit from './fit';
 
 class MockTerminal {}
 
diff --git a/src/addons/fit/fit.ts b/src/addons/fit/fit.ts
index b87ccc07..f037b540 100644
--- a/src/addons/fit/fit.ts
+++ b/src/addons/fit/fit.ts
@@ -13,28 +13,33 @@
  *          row and truncate its width with the current number of columns).
  */
 
-export function proposeGeometry(term) {
+export interface IGeometry {
+  rows: number;
+  cols: number;
+}
+
+export function proposeGeometry(term: any): IGeometry {
   if (!term.element.parentElement) {
     return null;
   }
-  var parentElementStyle = window.getComputedStyle(term.element.parentElement);
-  var parentElementHeight = parseInt(parentElementStyle.getPropertyValue('height'));
-  var parentElementWidth = Math.max(0, parseInt(parentElementStyle.getPropertyValue('width')) - 17);
-  var elementStyle = window.getComputedStyle(term.element);
-  var elementPaddingVer = parseInt(elementStyle.getPropertyValue('padding-top')) + parseInt(elementStyle.getPropertyValue('padding-bottom'));
-  var elementPaddingHor = parseInt(elementStyle.getPropertyValue('padding-right')) + parseInt(elementStyle.getPropertyValue('padding-left'));
-  var availableHeight = parentElementHeight - elementPaddingVer;
-  var availableWidth = parentElementWidth - elementPaddingHor;
-  var geometry = {
+  const parentElementStyle = window.getComputedStyle(term.element.parentElement);
+  const parentElementHeight = parseInt(parentElementStyle.getPropertyValue('height'));
+  const parentElementWidth = Math.max(0, parseInt(parentElementStyle.getPropertyValue('width')) - 17);
+  const elementStyle = window.getComputedStyle(term.element);
+  const elementPaddingVer = parseInt(elementStyle.getPropertyValue('padding-top')) + parseInt(elementStyle.getPropertyValue('padding-bottom'));
+  const elementPaddingHor = parseInt(elementStyle.getPropertyValue('padding-right')) + parseInt(elementStyle.getPropertyValue('padding-left'));
+  const availableHeight = parentElementHeight - elementPaddingVer;
+  const availableWidth = parentElementWidth - elementPaddingHor;
+  const geometry = {
     cols: Math.floor(availableWidth / term.renderer.dimensions.actualCellWidth),
     rows: Math.floor(availableHeight / term.renderer.dimensions.actualCellHeight)
   };
 
   return geometry;
-};
+}
 
-export function fit(term) {
-  var geometry = proposeGeometry(term);
+export function fit(term: any): void {
+  const geometry = proposeGeometry(term);
   if (geometry) {
     // Force a full render
     if (term.rows !== geometry.rows || term.cols !== geometry.cols) {
@@ -44,12 +49,12 @@ export function fit(term) {
   }
 };
 
-export function apply(terminalConstructor) {
-  terminalConstructor.prototype.proposeGeometry = function() {
+export function apply(terminalConstructor: any): void {
+  terminalConstructor.prototype.proposeGeometry = function (): IGeometry {
     return proposeGeometry(this);
-  }
+  };
 
-  terminalConstructor.prototype.fit = function() {
-    return fit(this);
-  }
+  terminalConstructor.prototype.fit = function (): void {
+    fit(this);
+  };
 }
diff --git a/src/addons/fullscreen/fullscreen.test.ts b/src/addons/fullscreen/fullscreen.test.ts
index c77ea75c..9326ac4e 100644
--- a/src/addons/fullscreen/fullscreen.test.ts
+++ b/src/addons/fullscreen/fullscreen.test.ts
@@ -5,7 +5,7 @@
 
 import { assert, expect } from 'chai';
 
-import * as fullscreen from './fullscreen'
+import * as fullscreen from './fullscreen';
 
 class MockTerminal {}
 
diff --git a/src/addons/fullscreen/fullscreen.ts b/src/addons/fullscreen/fullscreen.ts
index 31ab5189..0eb61ea1 100644
--- a/src/addons/fullscreen/fullscreen.ts
+++ b/src/addons/fullscreen/fullscreen.ts
@@ -8,10 +8,10 @@
  * @param {Terminal} term - The terminal to toggle full screen mode
  * @param {boolean} fullscreen - Toggle fullscreen on (true) or off (false)
  */
-export function toggleFullScreen(term, fullscreen) {
-  var fn;
+export function toggleFullScreen(term: any, fullscreen: boolean): void {
+  let fn;
 
-  if (typeof fullscreen == 'undefined') {
+  if (typeof fullscreen === 'undefined') {
     fn = (term.element.classList.contains('fullscreen')) ? 'remove' : 'add';
   } else if (!fullscreen) {
     fn = 'remove';
@@ -22,8 +22,8 @@ export function toggleFullScreen(term, fullscreen) {
   term.element.classList[fn]('fullscreen');
 };
 
-export function apply(terminalConstructor) {
-  terminalConstructor.prototype.toggleFullScreen = function (fullscreen) {
-    return toggleFullScreen(this, fullscreen);
+export function apply(terminalConstructor: any): void {
+  terminalConstructor.prototype.toggleFullScreen = function (fullscreen: boolean): void {
+    toggleFullScreen(this, fullscreen);
   };
 }
diff --git a/src/addons/search/search.ts b/src/addons/search/search.ts
index 480fea7f..375b86f4 100644
--- a/src/addons/search/search.ts
+++ b/src/addons/search/search.ts
@@ -32,12 +32,12 @@ export function findPrevious(terminal: any, term: string): boolean {
   return (<SearchHelper>terminal.searchHelper).findPrevious(term);
 };
 
-export function apply(terminalConstructor) {
-  terminalConstructor.prototype.findNext = function(term) {
+export function apply(terminalConstructor: any): void {
+  terminalConstructor.prototype.findNext = function(term: any): boolean {
     return findNext(this, term);
-  }
+  };
 
-  terminalConstructor.prototype.findPrevious = function(term) {
+  terminalConstructor.prototype.findPrevious = function(term: any): boolean {
     return findPrevious(this, term);
-  }
+  };
 }
diff --git a/src/addons/terminado/terminado.test.ts b/src/addons/terminado/terminado.test.ts
index fe059898..e258bd7c 100644
--- a/src/addons/terminado/terminado.test.ts
+++ b/src/addons/terminado/terminado.test.ts
@@ -5,7 +5,7 @@
 
 import { assert, expect } from 'chai';
 
-import * as terminado from './terminado'
+import * as terminado from './terminado';
 
 class MockTerminal {}
 
diff --git a/src/addons/terminado/terminado.ts b/src/addons/terminado/terminado.ts
index 9a7c7ad6..afd7277c 100644
--- a/src/addons/terminado/terminado.ts
+++ b/src/addons/terminado/terminado.ts
@@ -17,16 +17,16 @@
  *                             should happen instantly or at a maximum
  *                             frequency of 1 rendering per 10ms.
  */
-export function terminadoAttach(term, socket, bidirectional, buffered) {
-  bidirectional = (typeof bidirectional == 'undefined') ? true : bidirectional;
+export function terminadoAttach(term: any, socket: WebSocket, bidirectional: boolean, buffered: boolean): void {
+  bidirectional = (typeof bidirectional === 'undefined') ? true : bidirectional;
   term.socket = socket;
 
-  term._flushBuffer = function() {
+  term._flushBuffer = () => {
     term.write(term._attachSocketBuffer);
     term._attachSocketBuffer = null;
   };
 
-  term._pushToBuffer = function(data) {
+  term._pushToBuffer = (data) => {
     if (term._attachSocketBuffer) {
       term._attachSocketBuffer += data;
     } else {
@@ -35,9 +35,9 @@ export function terminadoAttach(term, socket, bidirectional, buffered) {
     }
   };
 
-  term._getMessage = function(ev) {
-    var data = JSON.parse(ev.data)
-    if( data[0] == "stdout" ) {
+  term._getMessage = (ev: MessageEvent) => {
+    const data = JSON.parse(ev.data);
+    if (data[0] === 'stdout') {
       if (buffered) {
         term._pushToBuffer(data[1]);
       } else {
@@ -46,11 +46,11 @@ export function terminadoAttach(term, socket, bidirectional, buffered) {
     }
   };
 
-  term._sendData = function(data) {
+  term._sendData = (data: string) => {
     socket.send(JSON.stringify(['stdin', data]));
   };
 
-  term._setSize = function(size) {
+  term._setSize = (size: {rows: number, cols: number}) => {
     socket.send(JSON.stringify(['set_size', size.rows, size.cols]));
   };
 
@@ -72,10 +72,10 @@ export function terminadoAttach(term, socket, bidirectional, buffered) {
  * @param {WebSocket} socket - The socket from which to detach the current
  *                             terminal.
  */
-export function terminadoDetach(term, socket) {
+export function terminadoDetach(term: any, socket: WebSocket): void {
   term.off('data', term._sendData);
 
-  socket = (typeof socket == 'undefined') ? term.socket : socket;
+  socket = (typeof socket === 'undefined') ? term.socket : socket;
 
   if (socket) {
     socket.removeEventListener('message', term._getMessage);
@@ -84,7 +84,7 @@ export function terminadoDetach(term, socket) {
   delete term.socket;
 };
 
-export function apply(terminalConstructor) {
+export function apply(terminalConstructor: any): void {
   /**
    * Attaches the current terminal to the given socket
    *
@@ -95,7 +95,7 @@ export function apply(terminalConstructor) {
    *                             should happen instantly or at a maximum
    *                             frequency of 1 rendering per 10ms.
    */
-  terminalConstructor.prototype.terminadoAttach = function(socket, bidirectional, buffered) {
+  terminalConstructor.prototype.terminadoAttach = function(socket: WebSocket, bidirectional: boolean, buffered: boolean): void {
     return terminadoAttach(this, socket, bidirectional, buffered);
   };
 
@@ -105,7 +105,7 @@ export function apply(terminalConstructor) {
    * @param {WebSocket} socket - The socket from which to detach the current
    *                             terminal.
    */
-  terminalConstructor.prototype.terminadoDetach = function(socket) {
+  terminalConstructor.prototype.terminadoDetach = function(socket: WebSocket): void {
     return terminadoDetach(this, socket);
   };
 }
diff --git a/src/addons/winptyCompat/winptyCompat.test.ts b/src/addons/winptyCompat/winptyCompat.test.ts
index 21e54e56..73761fc9 100644
--- a/src/addons/winptyCompat/winptyCompat.test.ts
+++ b/src/addons/winptyCompat/winptyCompat.test.ts
@@ -5,7 +5,7 @@
 
 import { assert, expect } from 'chai';
 
-import * as winptyCompat from './winptyCompat'
+import * as winptyCompat from './winptyCompat';
 
 class MockTerminal {}
 
diff --git a/src/addons/winptyCompat/winptyCompat.ts b/src/addons/winptyCompat/winptyCompat.ts
index 723bf011..b594355b 100644
--- a/src/addons/winptyCompat/winptyCompat.ts
+++ b/src/addons/winptyCompat/winptyCompat.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-export function winptyCompatInit(terminal): void {
+export function winptyCompatInit(terminal: any): void {
     // Don't do anything when the platform is not Windows
     const isWindows = ['Windows', 'Win16', 'Win32', 'WinCE'].indexOf(navigator.platform) >= 0;
     if (!isWindows) {
@@ -31,7 +31,7 @@ export function winptyCompatInit(terminal): void {
     });
 }
 
-export function apply(terminalConstructor) {
+export function apply(terminalConstructor: any): void {
   terminalConstructor.prototype.winptyCompatInit = function(): void {
     winptyCompatInit(this);
   };
diff --git a/src/addons/zmodem/zmodem.test.ts b/src/addons/zmodem/zmodem.test.ts
index 3cb28316..7646b7cc 100644
--- a/src/addons/zmodem/zmodem.test.ts
+++ b/src/addons/zmodem/zmodem.test.ts
@@ -5,7 +5,7 @@
 
 import { assert, expect } from 'chai';
 
-import * as zmodem from './zmodem'
+import * as zmodem from './zmodem';
 
 class MockTerminal {}
 
diff --git a/src/addons/zmodem/zmodem.ts b/src/addons/zmodem/zmodem.ts
index 57bdde3c..f1e6050f 100644
--- a/src/addons/zmodem/zmodem.ts
+++ b/src/addons/zmodem/zmodem.ts
@@ -29,45 +29,38 @@
 
 let Zmodem;
 
-export function zmodemAttach(term, ws, opts) {
-  if (!opts) opts = {};
+export interface IZModemOptions {
+  noTerminalWriteOutsideSession?: boolean;
+}
 
-  var senderFunc = function _ws_sender_func(octets) {
-    ws.send(new Uint8Array(octets));
-  };
+export function zmodemAttach(term: any, ws: WebSocket, opts: IZModemOptions = {}): void {
+  const senderFunc = (octets: ArrayLike<number>) => ws.send(new Uint8Array(octets));
 
-  var zsentry;
+  let zsentry;
 
-  function _shouldWrite() {
+  function _shouldWrite(): boolean {
     return !!zsentry.get_confirmed_session() || !opts.noTerminalWriteOutsideSession;
   }
 
-  zsentry = new Zmodem.Sentry( {
-    to_terminal: function _to_terminal(octets) {
+  zsentry = new Zmodem.Sentry({
+    to_terminal: (octets: ArrayLike<number>) => {
       if (_shouldWrite()) {
         term.write(
           String.fromCharCode.apply(String, octets)
         );
       }
     },
-
     sender: senderFunc,
+    on_retract: () => term.emit('zmodemRetract'),
+    on_detect: (detection: any) => term.emit('zmodemDetect', detection)
+  });
 
-    on_retract: function _on_retract() {
-      term.emit('zmodemRetract');
-    },
+  function handleWSMessage(evt: MessageEvent): void {
 
-    on_detect: function _on_detect(detection) {
-      term.emit('zmodemDetect', detection);
-    },
-  } );
-
-  function handleWSMessage(evt) {
-
-    //In testing with xterm.js’s demo the first message was
-    //always text even if the rest were binary. While that
-    //may be specific to xterm.js’s demo, ultimately we
-    //should reject anything that isn’t binary.
+    // In testing with xterm.js’s demo the first message was
+    // always text even if the rest were binary. While that
+    // may be specific to xterm.js’s demo, ultimately we
+    // should reject anything that isn’t binary.
     if (typeof evt.data === 'string') {
       if (_shouldWrite()) {
         term.write(evt.data);
@@ -82,9 +75,9 @@ export function zmodemAttach(term, ws, opts) {
   ws.addEventListener('message', handleWSMessage);
 }
 
-export function apply(terminalConstructor) {
-  Zmodem = (typeof window == 'object') ? (<any>window).ZModem : {Browser: null};  // Nullify browser for tests
+export function apply(terminalConstructor: any): void {
+  Zmodem = (typeof window === 'object') ? (<any>window).ZModem : {Browser: null};  // Nullify browser for tests
 
   terminalConstructor.prototype.zmodemAttach = zmodemAttach.bind(this, this);
-  terminalConstructor.prototype.zmodemBrowser = Zmodem.Browser
+  terminalConstructor.prototype.zmodemBrowser = Zmodem.Browser;
 }