diff --git a/addons/xterm-addon-webgl/src/WebglRenderer.ts b/addons/xterm-addon-webgl/src/WebglRenderer.ts
index 0333fd20..ac997c96 100644
--- a/addons/xterm-addon-webgl/src/WebglRenderer.ts
+++ b/addons/xterm-addon-webgl/src/WebglRenderer.ts
@@ -3,7 +3,6 @@
  * @license MIT
  */
 
-import { ITerminal } from '../../../src/Types';
 import { GlyphRenderer } from './GlyphRenderer';
 import { LinkRenderLayer } from './renderLayer/LinkRenderLayer';
 import { CursorRenderLayer } from './renderLayer/CursorRenderLayer';
@@ -17,7 +16,7 @@ import { NULL_CELL_CODE } from 'common/buffer/Constants';
 import { Terminal, IEvent } from 'xterm';
 import { IRenderLayer } from './renderLayer/Types';
 import { IRenderDimensions, IRenderer, IRequestRedrawEvent } from 'browser/renderer/Types';
-import { IColorSet } from 'browser/Types';
+import { ITerminal, IColorSet } from 'browser/Types';
 import { EventEmitter } from 'common/EventEmitter';
 import { CellData } from 'common/buffer/CellData';
 
@@ -52,8 +51,8 @@ export class WebglRenderer extends Disposable implements IRenderer {
     this._core = (this._terminal as any)._core;
 
     this._renderLayers = [
-      new LinkRenderLayer(this._core.screenElement, 2, this._colors, this._core),
-      new CursorRenderLayer(this._core.screenElement, 3, this._colors, this._onRequestRedraw)
+      new LinkRenderLayer(this._core.screenElement!, 2, this._colors, this._core),
+      new CursorRenderLayer(this._core.screenElement!, 3, this._colors, this._onRequestRedraw)
     ];
     this.dimensions = {
       scaledCharWidth: 0,
@@ -83,7 +82,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
     if (!this._gl) {
       throw new Error('WebGL2 not supported ' + this._gl);
     }
-    this._core.screenElement.appendChild(this._canvas);
+    this._core.screenElement!.appendChild(this._canvas);
 
     this._rectangleRenderer = new RectangleRenderer(this._terminal, this._colors, this._gl, this.dimensions);
     this._glyphRenderer = new GlyphRenderer(this._terminal, this._colors, this._gl, this.dimensions);
@@ -91,12 +90,12 @@ export class WebglRenderer extends Disposable implements IRenderer {
     // Update dimensions and acquire char atlas
     this.onCharSizeChanged();
 
-    this._isAttached = document.body.contains(this._core.screenElement);
+    this._isAttached = document.body.contains(this._core.screenElement!);
   }
 
   public dispose(): void {
     this._renderLayers.forEach(l => l.dispose());
-    this._core.screenElement.removeChild(this._canvas);
+    this._core.screenElement!.removeChild(this._canvas);
     super.dispose();
   }
 
@@ -150,8 +149,8 @@ export class WebglRenderer extends Disposable implements IRenderer {
     this._canvas.style.height = `${this.dimensions.canvasHeight}px`;
 
     // Resize the screen
-    this._core.screenElement.style.width = `${this.dimensions.canvasWidth}px`;
-    this._core.screenElement.style.height = `${this.dimensions.canvasHeight}px`;
+    this._core.screenElement!.style.width = `${this.dimensions.canvasWidth}px`;
+    this._core.screenElement!.style.height = `${this.dimensions.canvasHeight}px`;
     this._glyphRenderer.setDimensions(this.dimensions);
     this._glyphRenderer.onResize();
 
@@ -229,7 +228,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
 
   public renderRows(start: number, end: number): void {
     if (!this._isAttached) {
-      if (document.body.contains(this._core.screenElement) && (this._core as any)._charSizeService.width && (this._core as any)._charSizeService.height) {
+      if (document.body.contains(this._core.screenElement!) && (this._core as any)._charSizeService.width && (this._core as any)._charSizeService.height) {
         this._updateDimensions();
         this._refreshCharAtlas();
         this._isAttached = true;
diff --git a/addons/xterm-addon-webgl/src/renderLayer/LinkRenderLayer.ts b/addons/xterm-addon-webgl/src/renderLayer/LinkRenderLayer.ts
index a095b4ae..8f6b3e6d 100644
--- a/addons/xterm-addon-webgl/src/renderLayer/LinkRenderLayer.ts
+++ b/addons/xterm-addon-webgl/src/renderLayer/LinkRenderLayer.ts
@@ -7,9 +7,8 @@ import { Terminal } from 'xterm';
 import { BaseRenderLayer } from './BaseRenderLayer';
 import { INVERTED_DEFAULT_COLOR } from 'browser/renderer/atlas/Constants';
 import { is256Color } from '../atlas/CharAtlasUtils';
-import { IColorSet, ILinkifierEvent, ILinkifier, ILinkifier2 } from 'browser/Types';
+import { ITerminal, IColorSet, ILinkifierEvent } from 'browser/Types';
 import { IRenderDimensions } from 'browser/renderer/Types';
-import { ITerminal } from '../../../../src/Types';
 
 export class LinkRenderLayer extends BaseRenderLayer {
   private _state: ILinkifierEvent | undefined;
diff --git a/src/TestUtils.test.ts b/src/TestUtils.test.ts
index 965acc88..102a5353 100644
--- a/src/TestUtils.test.ts
+++ b/src/TestUtils.test.ts
@@ -4,7 +4,6 @@
  */
 
 import { IRenderer, IRenderDimensions, CharacterJoinerHandler, IRequestRedrawEvent } from 'browser/renderer/Types';
-import { ICompositionHelper, ITerminal, IBrowser } from './Types';
 import { IBuffer, IBufferStringIterator, IBufferSet } from 'common/buffer/Types';
 import { IBufferLine, ICellData, IAttributeData, ICircularList, XtermListener, ICharset, ITerminalOptions } from 'common/Types';
 import { Buffer } from 'common/buffer/Buffer';
@@ -12,7 +11,7 @@ import * as Browser from 'common/Platform';
 import { IDisposable, IMarker, IEvent, ISelectionPosition, ILinkProvider } from 'xterm';
 import { Terminal } from './browser/Terminal';
 import { AttributeData } from 'common/buffer/AttributeData';
-import { IColorManager, IColorSet, ILinkMatcherOptions, ILinkifier, IViewport, ILinkifier2 } from 'browser/Types';
+import { IColorManager, IColorSet, ILinkMatcherOptions, ILinkifier, IViewport, ILinkifier2, ICompositionHelper, ITerminal, IBrowser } from 'browser/Types';
 import { IOptionsService, IUnicodeService } from 'common/services/Services';
 import { IParams, IFunctionIdentifier } from 'common/parser/Types';
 import { ISelectionService } from 'browser/services/Services';
diff --git a/src/browser/AccessibilityManager.ts b/src/browser/AccessibilityManager.ts
index b613e9ba..2a34d6a3 100644
--- a/src/browser/AccessibilityManager.ts
+++ b/src/browser/AccessibilityManager.ts
@@ -106,7 +106,7 @@ export class AccessibilityManager extends Disposable {
 
   public dispose(): void {
     super.dispose();
-    this._terminal.element.removeChild(this._accessibilityTreeRoot);
+    this._terminal.element?.removeChild(this._accessibilityTreeRoot);
     this._rowElements.length = 0;
   }
 
diff --git a/src/browser/Linkifier2.ts b/src/browser/Linkifier2.ts
index 54812169..458b1bff 100644
--- a/src/browser/Linkifier2.ts
+++ b/src/browser/Linkifier2.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { ILinkifier2, ILinkProvider, IBufferCellPosition, ILink, ILinkifierEvent, ILinkDecorations } from './Types';
+import { ILinkifier2, ILinkProvider, IBufferCellPosition, ILink, ILinkifierEvent, ILinkDecorations } from 'browser/Types';
 import { IDisposable } from 'common/Types';
 import { IMouseService, IRenderService } from './services/Services';
 import { IBufferService } from 'common/services/Services';
diff --git a/src/browser/Terminal.ts b/src/browser/Terminal.ts
index 2c22a12c..7f3ead61 100644
--- a/src/browser/Terminal.ts
+++ b/src/browser/Terminal.ts
@@ -21,7 +21,7 @@
  *   http://linux.die.net/man/7/urxvt
  */
 
-import { ICompositionHelper, ITerminal, IBrowser, CustomKeyEventHandler } from '../Types';
+import { ICompositionHelper, ITerminal, IBrowser, CustomKeyEventHandler, ILinkifier, IMouseZoneManager, LinkMatcherHandler, ILinkMatcherOptions, IViewport, ILinkifier2 } from 'browser/Types';
 import { IRenderer, CharacterJoinerHandler } from 'browser/renderer/Types';
 import { CompositionHelper } from 'browser/input/CompositionHelper';
 import { Viewport } from 'browser/Viewport';
@@ -49,41 +49,40 @@ import { ICharSizeService, IRenderService, IMouseService, ISelectionService, ISo
 import { CharSizeService } from 'browser/services/CharSizeService';
 import { IBuffer } from 'common/buffer/Types';
 import { MouseService } from 'browser/services/MouseService';
-import { ILinkifier, IMouseZoneManager, LinkMatcherHandler, ILinkMatcherOptions, IViewport, ILinkifier2 } from 'browser/Types';
 import { Linkifier2 } from 'browser/Linkifier2';
 import { CoreBrowserService } from 'browser/services/CoreBrowserService';
 import { CoreTerminal } from 'common/CoreTerminal';
+import { ITerminalOptions as IInitializedTerminalOptions } from 'common/services/Services';
 
 // Let it work inside Node.js for automated testing purposes.
-const document = (typeof window !== 'undefined') ? window.document : null;
-
+const document: Document = (typeof window !== 'undefined') ? window.document : null as any;
 
 export class Terminal extends CoreTerminal implements ITerminal {
-  public textarea: HTMLTextAreaElement;
-  public element: HTMLElement;
-  public screenElement: HTMLElement;
+  public textarea: HTMLTextAreaElement | undefined;
+  public element: HTMLElement | undefined;
+  public screenElement: HTMLElement | undefined;
 
-  private _document: Document;
-  private _viewportScrollArea: HTMLElement;
-  private _viewportElement: HTMLElement;
-  private _helperContainer: HTMLElement;
-  private _compositionView: HTMLElement;
+  private _document: Document | undefined;
+  private _viewportScrollArea: HTMLElement | undefined;
+  private _viewportElement: HTMLElement | undefined;
+  private _helperContainer: HTMLElement | undefined;
+  private _compositionView: HTMLElement | undefined;
 
-  private _visualBellTimer: number;
+  // private _visualBellTimer: number;
 
   public browser: IBrowser = <any>Browser;
 
   // TODO: We should remove options once components adopt optionsService
-  public get options(): ITerminalOptions { return this.optionsService.options; }
+  public get options(): IInitializedTerminalOptions { return this.optionsService.options; }
 
-  private _customKeyEventHandler: CustomKeyEventHandler;
+  private _customKeyEventHandler: CustomKeyEventHandler | undefined;
 
   // browser services
-  private _charSizeService: ICharSizeService;
-  private _mouseService: IMouseService;
-  private _renderService: IRenderService;
-  private _selectionService: ISelectionService;
-  private _soundService: ISoundService;
+  private _charSizeService: ICharSizeService | undefined;
+  private _mouseService: IMouseService | undefined;
+  private _renderService: IRenderService | undefined;
+  private _selectionService: ISelectionService | undefined;
+  private _soundService: ISoundService | undefined;
 
   /**
    * Records whether the keydown event has already been handled and triggered a data event, if so
@@ -94,12 +93,12 @@ export class Terminal extends CoreTerminal implements ITerminal {
 
   public linkifier: ILinkifier;
   public linkifier2: ILinkifier2;
-  public viewport: IViewport;
-  private _compositionHelper: ICompositionHelper;
-  private _mouseZoneManager: IMouseZoneManager;
-  private _accessibilityManager: AccessibilityManager;
-  private _colorManager: ColorManager;
-  private _theme: ITheme;
+  public viewport: IViewport | undefined;
+  private _compositionHelper: ICompositionHelper | undefined;
+  private _mouseZoneManager: IMouseZoneManager | undefined;
+  private _accessibilityManager: AccessibilityManager | undefined;
+  private _colorManager: ColorManager | undefined;
+  private _theme: ITheme | undefined;
 
   private _onCursorMove = new EventEmitter<void>();
   public get onCursorMove(): IEvent<void> { return this._onCursorMove.event; }
@@ -140,6 +139,10 @@ export class Terminal extends CoreTerminal implements ITerminal {
 
     this._setup();
 
+    this.linkifier = this._instantiationService.createInstance(Linkifier);
+    this.linkifier2 = this._instantiationService.createInstance(Linkifier2);
+
+    // Setup InputHandler listeners
     this.register(this._inputHandler.onRequestBell(() => this.bell()));
     this.register(this._inputHandler.onRequestRefreshRows((start, end) => this.refresh(start, end)));
     this.register(this._inputHandler.onRequestReset(() => this.reset()));
@@ -160,7 +163,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
     }
     super.dispose();
     this._renderService?.dispose();
-    this._customKeyEventHandler = null;
+    this._customKeyEventHandler = undefined;
     this.write = () => { };
     this.element?.parentNode?.removeChild(this.element);
   }
@@ -168,14 +171,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
   protected _setup(): void {
     super._setup();
 
-    this._customKeyEventHandler = null;
-
-    if (!this.linkifier) {
-      this.linkifier = this._instantiationService.createInstance(Linkifier);
-    }
-    if (!this.linkifier2) {
-      this.linkifier2 = this._instantiationService.createInstance(Linkifier2);
-    }
+    this._customKeyEventHandler = undefined;
   }
 
   /**
@@ -239,7 +235,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
           }
         } else {
           this._accessibilityManager?.dispose();
-          this._accessibilityManager = null;
+          this._accessibilityManager = undefined;
         }
         break;
       case 'tabStopWidth': this.buffers.setupTabStops(); break;
@@ -257,7 +253,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
       this._coreService.triggerDataEvent(C0.ESC + '[I');
     }
     this.updateCursorStyle(ev);
-    this.element.classList.add('focus');
+    this.element!.classList.add('focus');
     this._showCursor();
     this._onFocus.fire();
   }
@@ -267,7 +263,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
    * textarea.
    */
   public blur(): void {
-    return this.textarea.blur();
+    return this.textarea?.blur();
   }
 
   /**
@@ -276,12 +272,12 @@ export class Terminal extends CoreTerminal implements ITerminal {
   private _onTextAreaBlur(): void {
     // Text can safely be removed on blur. Doing it earlier could interfere with
     // screen readers reading it out.
-    this.textarea.value = '';
+    this.textarea!.value = '';
     this.refresh(this.buffer.y, this.buffer.y);
     if (this._coreService.decPrivateModes.sendFocus) {
       this._coreService.triggerDataEvent(C0.ESC + '[O');
     }
-    this.element.classList.remove('focus');
+    this.element!.classList.remove('focus');
     this._onBlur.fire();
   }
 
@@ -292,29 +288,29 @@ export class Terminal extends CoreTerminal implements ITerminal {
     this._bindKeys();
 
     // Bind clipboard functionality
-    this.register(addDisposableDomListener(this.element, 'copy', (event: ClipboardEvent) => {
+    this.register(addDisposableDomListener(this.element!, 'copy', (event: ClipboardEvent) => {
       // If mouse events are active it means the selection manager is disabled and
       // copy should be handled by the host program.
       if (!this.hasSelection()) {
         return;
       }
-      copyHandler(event, this._selectionService);
+      copyHandler(event, this._selectionService!);
     }));
-    const pasteHandlerWrapper = (event: ClipboardEvent): void => handlePasteEvent(event, this.textarea, this._coreService);
-    this.register(addDisposableDomListener(this.textarea, 'paste', pasteHandlerWrapper));
-    this.register(addDisposableDomListener(this.element, 'paste', pasteHandlerWrapper));
+    const pasteHandlerWrapper = (event: ClipboardEvent): void => handlePasteEvent(event, this.textarea!, this._coreService);
+    this.register(addDisposableDomListener(this.textarea!, 'paste', pasteHandlerWrapper));
+    this.register(addDisposableDomListener(this.element!, 'paste', pasteHandlerWrapper));
 
     // Handle right click context menus
     if (Browser.isFirefox) {
       // Firefox doesn't appear to fire the contextmenu event on right click
-      this.register(addDisposableDomListener(this.element, 'mousedown', (event: MouseEvent) => {
+      this.register(addDisposableDomListener(this.element!, 'mousedown', (event: MouseEvent) => {
         if (event.button === 2) {
-          rightClickHandler(event, this.textarea, this.screenElement, this._selectionService, this.options.rightClickSelectsWord);
+          rightClickHandler(event, this.textarea!, this.screenElement!, this._selectionService!, this.options.rightClickSelectsWord);
         }
       }));
     } else {
-      this.register(addDisposableDomListener(this.element, 'contextmenu', (event: MouseEvent) => {
-        rightClickHandler(event, this.textarea, this.screenElement, this._selectionService, this.options.rightClickSelectsWord);
+      this.register(addDisposableDomListener(this.element!, 'contextmenu', (event: MouseEvent) => {
+        rightClickHandler(event, this.textarea!, this.screenElement!, this._selectionService!, this.options.rightClickSelectsWord);
       }));
     }
 
@@ -324,9 +320,9 @@ export class Terminal extends CoreTerminal implements ITerminal {
     if (Browser.isLinux) {
       // Use auxclick event over mousedown the latter doesn't seem to work. Note
       // that the regular click event doesn't fire for the middle mouse button.
-      this.register(addDisposableDomListener(this.element, 'auxclick', (event: MouseEvent) => {
+      this.register(addDisposableDomListener(this.element!, 'auxclick', (event: MouseEvent) => {
         if (event.button === 1) {
-          moveTextAreaUnderMouseCursor(event, this.textarea, this.screenElement);
+          moveTextAreaUnderMouseCursor(event, this.textarea!, this.screenElement!);
         }
       }));
     }
@@ -336,13 +332,13 @@ export class Terminal extends CoreTerminal implements ITerminal {
    * Apply key handling to the terminal
    */
   private _bindKeys(): void {
-    this.register(addDisposableDomListener(this.textarea, 'keyup', (ev: KeyboardEvent) => this._keyUp(ev), true));
-    this.register(addDisposableDomListener(this.textarea, 'keydown', (ev: KeyboardEvent) => this._keyDown(ev), true));
-    this.register(addDisposableDomListener(this.textarea, 'keypress', (ev: KeyboardEvent) => this._keyPress(ev), true));
-    this.register(addDisposableDomListener(this.textarea, 'compositionstart', () => this._compositionHelper.compositionstart()));
-    this.register(addDisposableDomListener(this.textarea, 'compositionupdate', (e: CompositionEvent) => this._compositionHelper.compositionupdate(e)));
-    this.register(addDisposableDomListener(this.textarea, 'compositionend', () => this._compositionHelper.compositionend()));
-    this.register(this.onRender(() => this._compositionHelper.updateCompositionElements()));
+    this.register(addDisposableDomListener(this.textarea!, 'keyup', (ev: KeyboardEvent) => this._keyUp(ev), true));
+    this.register(addDisposableDomListener(this.textarea!, 'keydown', (ev: KeyboardEvent) => this._keyDown(ev), true));
+    this.register(addDisposableDomListener(this.textarea!, 'keypress', (ev: KeyboardEvent) => this._keyPress(ev), true));
+    this.register(addDisposableDomListener(this.textarea!, 'compositionstart', () => this._compositionHelper!.compositionstart()));
+    this.register(addDisposableDomListener(this.textarea!, 'compositionupdate', (e: CompositionEvent) => this._compositionHelper!.compositionupdate(e)));
+    this.register(addDisposableDomListener(this.textarea!, 'compositionend', () => this._compositionHelper!.compositionend()));
+    this.register(this.onRender(() => this._compositionHelper!.updateCompositionElements()));
     this.register(this.onRender(e => this._queueLinkification(e.start, e.end)));
   }
 
@@ -360,7 +356,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
       this._logService.debug('Terminal.open was called on an element that was not attached to the DOM');
     }
 
-    this._document = parent.ownerDocument;
+    this._document = parent.ownerDocument!;
 
     // Create main element container
     this.element = this._document.createElement('div');
@@ -416,16 +412,15 @@ export class Terminal extends CoreTerminal implements ITerminal {
     this.element.appendChild(fragment);
 
     this._theme = this.options.theme || this._theme;
-    this.options.theme = undefined;
     this._colorManager = new ColorManager(document, this.options.allowTransparency);
-    this.optionsService.onOptionChange(e => this._colorManager.onOptionsChange(e));
+    this.optionsService.onOptionChange(e => this._colorManager!.onOptionsChange(e));
     this._colorManager.setTheme(this._theme);
 
     const renderer = this._createRenderer();
     this._renderService = this._instantiationService.createInstance(RenderService, renderer, this.rows, this.screenElement);
     this._instantiationService.setService(IRenderService, this._renderService);
     this._renderService.onRenderedBufferChange(e => this._onRender.fire(e));
-    this.onResize(e => this._renderService.resize(e.cols, e.rows));
+    this.onResize(e => this._renderService!.resize(e.cols, e.rows));
 
     this._soundService = this._instantiationService.createInstance(SoundService);
     this._instantiationService.setService(ISoundService, this._soundService);
@@ -438,14 +433,14 @@ export class Terminal extends CoreTerminal implements ITerminal {
       this._viewportScrollArea
     );
     this.viewport.onThemeChange(this._colorManager.colors);
-    this.register(this._inputHandler.onRequestSyncScrollBar(() => this.viewport.syncScrollArea()));
+    this.register(this._inputHandler.onRequestSyncScrollBar(() => this.viewport!.syncScrollArea()));
     this.register(this.viewport);
 
-    this.register(this.onCursorMove(() => this._renderService.onCursorMove()));
-    this.register(this.onResize(() => this._renderService.onResize(this.cols, this.rows)));
-    this.register(this.onBlur(() => this._renderService.onBlur()));
-    this.register(this.onFocus(() => this._renderService.onFocus()));
-    this.register(this._renderService.onDimensionsChange(() => this.viewport.syncScrollArea()));
+    this.register(this.onCursorMove(() => this._renderService!.onCursorMove()));
+    this.register(this.onResize(() => this._renderService!.onResize(this.cols, this.rows)));
+    this.register(this.onBlur(() => this._renderService!.onBlur()));
+    this.register(this.onFocus(() => this._renderService!.onFocus()));
+    this.register(this._renderService.onDimensionsChange(() => this.viewport!.syncScrollArea()));
 
     this._selectionService = this._instantiationService.createInstance(SelectionService,
       (amount: number, suppressEvent: boolean) => this.scrollLines(amount, suppressEvent),
@@ -453,29 +448,29 @@ export class Terminal extends CoreTerminal implements ITerminal {
       this.screenElement);
     this._instantiationService.setService(ISelectionService, this._selectionService);
     this.register(this._selectionService.onSelectionChange(() => this._onSelectionChange.fire()));
-    this.register(this._selectionService.onRedrawRequest(e => this._renderService.onSelectionChanged(e.start, e.end, e.columnSelectMode)));
+    this.register(this._selectionService.onRedrawRequest(e => this._renderService!.onSelectionChanged(e.start, e.end, e.columnSelectMode)));
     this.register(this._selectionService.onLinuxMouseSelection(text => {
       // If there's a new selection, put it into the textarea, focus and select it
       // in order to register it as a selection on the OS. This event is fired
       // only on Linux to enable middle click to paste selection.
-      this.textarea.value = text;
-      this.textarea.focus();
-      this.textarea.select();
+      this.textarea!.value = text;
+      this.textarea!.focus();
+      this.textarea!.select();
     }));
     this.register(this.onScroll(() => {
-      this.viewport.syncScrollArea();
-      this._selectionService.refresh();
+      this.viewport!.syncScrollArea();
+      this._selectionService!.refresh();
     }));
-    this.register(addDisposableDomListener(this._viewportElement, 'scroll', () => this._selectionService.refresh()));
+    this.register(addDisposableDomListener(this._viewportElement, 'scroll', () => this._selectionService!.refresh()));
 
     this._mouseZoneManager = this._instantiationService.createInstance(MouseZoneManager, this.element, this.screenElement);
     this.register(this._mouseZoneManager);
-    this.register(this.onScroll(() => this._mouseZoneManager.clearAll()));
+    this.register(this.onScroll(() => this._mouseZoneManager!.clearAll()));
     this.linkifier.attachToDom(this.element, this._mouseZoneManager);
     this.linkifier2.attachToDom(this.element, this._mouseService, this._renderService);
 
     // This event listener must be registered aftre MouseZoneManager is created
-    this.register(addDisposableDomListener(this.element, 'mousedown', (e: MouseEvent) => this._selectionService.onMouseDown(e)));
+    this.register(addDisposableDomListener(this.element, 'mousedown', (e: MouseEvent) => this._selectionService!.onMouseDown(e)));
 
     // apply mouse event classes set by escape codes before terminal was attached
     if (this._coreMouseService.areMouseEventsActive) {
@@ -507,8 +502,8 @@ export class Terminal extends CoreTerminal implements ITerminal {
 
   private _createRenderer(): IRenderer {
     switch (this.options.rendererType) {
-      case 'canvas': return this._instantiationService.createInstance(Renderer, this._colorManager.colors, this.screenElement, this.linkifier, this.linkifier2);
-      case 'dom': return this._instantiationService.createInstance(DomRenderer, this._colorManager.colors, this.element, this.screenElement, this._viewportElement, this.linkifier, this.linkifier2);
+      case 'canvas': return this._instantiationService.createInstance(Renderer, this._colorManager!.colors, this.screenElement!, this.linkifier, this.linkifier2);
+      case 'dom': return this._instantiationService.createInstance(DomRenderer, this._colorManager!.colors, this.element!, this.screenElement!, this._viewportElement!, this.linkifier, this.linkifier2);
       default: throw new Error(`Unrecognized rendererType "${this.options.rendererType}"`);
     }
   }
@@ -520,8 +515,8 @@ export class Terminal extends CoreTerminal implements ITerminal {
   private _setTheme(theme: ITheme): void {
     this._theme = theme;
     this._colorManager?.setTheme(theme);
-    this._renderService?.setColors(this._colorManager.colors);
-    this.viewport?.onThemeChange(this._colorManager.colors);
+    this._renderService?.setColors(this._colorManager!.colors);
+    this.viewport?.onThemeChange(this._colorManager!.colors);
   }
 
   /**
@@ -541,18 +536,18 @@ export class Terminal extends CoreTerminal implements ITerminal {
    */
   public bindMouse(): void {
     const self = this;
-    const el = this.element;
+    const el = this.element!;
 
     // send event to CoreMouseService
     function sendEvent(ev: MouseEvent | WheelEvent): boolean {
       // get mouse coordinates
-      const pos = self._mouseService.getRawByteCoords(ev, self.screenElement, self.cols, self.rows);
+      const pos = self._mouseService!.getRawByteCoords(ev, self.screenElement!, self.cols, self.rows);
       if (!pos) {
         return false;
       }
 
       let but: CoreMouseButton;
-      let action: CoreMouseAction;
+      let action: CoreMouseAction | undefined;
       switch ((<any>ev).overrideType || ev.type) {
         case 'mousemove':
           action = CoreMouseAction.MOVE;
@@ -621,14 +616,14 @@ export class Terminal extends CoreTerminal implements ITerminal {
       mousedrag: null,
       mousemove: null
     };
-    const eventListeners: { [key: string]: (ev: Event) => void } = {
+    const eventListeners: { [key: string]: (ev: any) => void | boolean } = {
       mouseup: (ev: MouseEvent) => {
         sendEvent(ev);
         if (!ev.buttons) {
           // if no other button is held remove global handlers
-          this._document.removeEventListener('mouseup', requestedEvents.mouseup);
+          this._document!.removeEventListener('mouseup', requestedEvents.mouseup!);
           if (requestedEvents.mousedrag) {
-            this._document.removeEventListener('mousemove', requestedEvents.mousedrag);
+            this._document!.removeEventListener('mousemove', requestedEvents.mousedrag);
           }
         }
         return this.cancel(ev);
@@ -657,18 +652,18 @@ export class Terminal extends CoreTerminal implements ITerminal {
         if (this.optionsService.options.logLevel === 'debug') {
           this._logService.debug('Binding to mouse events:', this._coreMouseService.explainEvents(events));
         }
-        this.element.classList.add('enable-mouse-events');
-        this._selectionService.disable();
+        this.element!.classList.add('enable-mouse-events');
+        this._selectionService!.disable();
       } else {
         this._logService.debug('Unbinding from mouse events.');
-        this.element.classList.remove('enable-mouse-events');
-        this._selectionService.enable();
+        this.element!.classList.remove('enable-mouse-events');
+        this._selectionService!.enable();
       }
 
       // add/remove handlers from requestedEvents
 
       if (!(events & CoreMouseEventType.MOVE)) {
-        el.removeEventListener('mousemove', requestedEvents.mousemove);
+        el.removeEventListener('mousemove', requestedEvents.mousemove!);
         requestedEvents.mousemove = null;
       } else if (!requestedEvents.mousemove) {
         el.addEventListener('mousemove', eventListeners.mousemove);
@@ -676,7 +671,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
       }
 
       if (!(events & CoreMouseEventType.WHEEL)) {
-        el.removeEventListener('wheel', requestedEvents.wheel);
+        el.removeEventListener('wheel', requestedEvents.wheel!);
         requestedEvents.wheel = null;
       } else if (!requestedEvents.wheel) {
         el.addEventListener('wheel', eventListeners.wheel);
@@ -684,14 +679,14 @@ export class Terminal extends CoreTerminal implements ITerminal {
       }
 
       if (!(events & CoreMouseEventType.UP)) {
-        this._document.removeEventListener('mouseup', requestedEvents.mouseup);
+        this._document!.removeEventListener('mouseup', requestedEvents.mouseup!);
         requestedEvents.mouseup = null;
       } else if (!requestedEvents.mouseup) {
         requestedEvents.mouseup = eventListeners.mouseup;
       }
 
       if (!(events & CoreMouseEventType.DRAG)) {
-        this._document.removeEventListener('mousemove', requestedEvents.mousedrag);
+        this._document!.removeEventListener('mousemove', requestedEvents.mousedrag!);
         requestedEvents.mousedrag = null;
       } else if (!requestedEvents.mousedrag) {
         requestedEvents.mousedrag = eventListeners.mousedrag;
@@ -710,7 +705,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
       // Don't send the mouse button to the pty if mouse events are disabled or
       // if the selection manager is having selection forced (ie. a modifier is
       // held).
-      if (!this._coreMouseService.areMouseEventsActive || this._selectionService.shouldForceSelection(ev)) {
+      if (!this._coreMouseService.areMouseEventsActive || this._selectionService!.shouldForceSelection(ev)) {
         return;
       }
 
@@ -721,10 +716,10 @@ export class Terminal extends CoreTerminal implements ITerminal {
       // Note: Other emulators also do this for 'mousedown' while a button
       // is held, we currently limit 'mousedown' to the terminal only.
       if (requestedEvents.mouseup) {
-        this._document.addEventListener('mouseup', requestedEvents.mouseup);
+        this._document!.addEventListener('mouseup', requestedEvents.mouseup);
       }
       if (requestedEvents.mousedrag) {
-        this._document.addEventListener('mousemove', requestedEvents.mousedrag);
+        this._document!.addEventListener('mousemove', requestedEvents.mousedrag);
       }
 
       return this.cancel(ev);
@@ -735,7 +730,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
         // Convert wheel events into up/down events when the buffer does not have scrollback, this
         // enables scrolling in apps hosted in the alt buffer such as vim or tmux.
         if (!this.buffer.hasScrollback) {
-          const amount = this.viewport.getLinesScrolled(ev);
+          const amount = this.viewport!.getLinesScrolled(ev);
 
           // Do nothing if there's no vertical scroll
           if (amount === 0) {
@@ -758,20 +753,20 @@ export class Terminal extends CoreTerminal implements ITerminal {
     // the shell for example
     this.register(addDisposableDomListener(el, 'wheel', (ev: WheelEvent) => {
       if (requestedEvents.wheel) return;
-      if (!this.viewport.onWheel(ev)) {
+      if (!this.viewport!.onWheel(ev)) {
         return this.cancel(ev);
       }
     }));
 
     this.register(addDisposableDomListener(el, 'touchstart', (ev: TouchEvent) => {
       if (this._coreMouseService.areMouseEventsActive) return;
-      this.viewport.onTouchStart(ev);
+      this.viewport!.onTouchStart(ev);
       return this.cancel(ev);
     }));
 
     this.register(addDisposableDomListener(el, 'touchmove', (ev: TouchEvent) => {
       if (this._coreMouseService.areMouseEventsActive) return;
-      if (!this.viewport.onTouchMove(ev)) {
+      if (!this.viewport!.onTouchMove(ev)) {
         return this.cancel(ev);
       }
     }));
@@ -802,9 +797,9 @@ export class Terminal extends CoreTerminal implements ITerminal {
    */
   public updateCursorStyle(ev: KeyboardEvent): void {
     if (this._selectionService && this._selectionService.shouldColumnSelect(ev)) {
-      this.element.classList.add('column-select');
+      this.element!.classList.add('column-select');
     } else {
-      this.element.classList.remove('column-select');
+      this.element!.classList.remove('column-select');
     }
   }
 
@@ -824,7 +819,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
   }
 
   public paste(data: string): void {
-    paste(data, this.textarea, this._coreService);
+    paste(data, this.textarea!, this._coreService);
   }
 
   /**
@@ -871,13 +866,13 @@ export class Terminal extends CoreTerminal implements ITerminal {
   }
 
   public registerCharacterJoiner(handler: CharacterJoinerHandler): number {
-    const joinerId = this._renderService.registerCharacterJoiner(handler);
+    const joinerId = this._renderService!.registerCharacterJoiner(handler);
     this.refresh(0, this.rows - 1);
     return joinerId;
   }
 
   public deregisterCharacterJoiner(joinerId: number): void {
-    if (this._renderService.deregisterCharacterJoiner(joinerId)) {
+    if (this._renderService!.deregisterCharacterJoiner(joinerId)) {
       this.refresh(0, this.rows - 1);
     }
   }
@@ -886,7 +881,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
     return this.buffer.markers;
   }
 
-  public addMarker(cursorYOffset: number): IMarker {
+  public addMarker(cursorYOffset: number): IMarker | undefined {
     // Disallow markers on the alt buffer
     if (this.buffer !== this.buffers.normal) {
       return;
@@ -909,7 +904,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
    * @param length The length of the selection.
    */
   public select(column: number, row: number, length: number): void {
-    this._selectionService.setSelection(column, row, length);
+    this._selectionService!.setSelection(column, row, length);
   }
 
   /**
@@ -921,15 +916,15 @@ export class Terminal extends CoreTerminal implements ITerminal {
   }
 
   public getSelectionPosition(): ISelectionPosition | undefined {
-    if (!this._selectionService.hasSelection) {
+    if (!this._selectionService || !this._selectionService.hasSelection) {
       return undefined;
     }
 
     return {
-      startColumn: this._selectionService.selectionStart[0],
-      startRow: this._selectionService.selectionStart[1],
-      endColumn: this._selectionService.selectionEnd[0],
-      endRow: this._selectionService.selectionEnd[1]
+      startColumn: this._selectionService.selectionStart![0],
+      startRow: this._selectionService.selectionStart![1],
+      endColumn: this._selectionService.selectionEnd![0],
+      endRow: this._selectionService.selectionEnd![1]
     };
   }
 
@@ -957,14 +952,14 @@ export class Terminal extends CoreTerminal implements ITerminal {
    *   - https://developer.mozilla.org/en-US/docs/DOM/KeyboardEvent
    * @param ev The keydown event to be handled.
    */
-  protected _keyDown(event: KeyboardEvent): boolean {
+  protected _keyDown(event: KeyboardEvent): boolean | undefined {
     this._keyDownHandled = false;
 
     if (this._customKeyEventHandler && this._customKeyEventHandler(event) === false) {
       return false;
     }
 
-    if (!this._compositionHelper.keydown(event)) {
+    if (!this._compositionHelper!.keydown(event)) {
       if (this.buffer.ybase !== this.buffer.ydisp) {
         this.scrollToBottom();
       }
@@ -1002,7 +997,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
     // will announce deleted characters. This will not work 100% of the time but it should cover
     // most scenarios.
     if (result.key === C0.ETX || result.key === C0.CR) {
-      this.textarea.value = '';
+      this.textarea!.value = '';
     }
 
     this._onKey.fire({ key: result.key, domEvent: event });
@@ -1095,16 +1090,16 @@ export class Terminal extends CoreTerminal implements ITerminal {
    */
   public bell(): void {
     if (this._soundBell()) {
-      this._soundService.playBellSound();
+      this._soundService!.playBellSound();
     }
 
-    if (this._visualBell()) {
-      this.element.classList.add('visual-bell-active');
-      clearTimeout(this._visualBellTimer);
-      this._visualBellTimer = window.setTimeout(() => {
-        this.element.classList.remove('visual-bell-active');
-      }, 200);
-    }
+    // if (this._visualBell()) {
+    //   this.element.classList.add('visual-bell-active');
+    //   clearTimeout(this._visualBellTimer);
+    //   this._visualBellTimer = window.setTimeout(() => {
+    //     this.element.classList.remove('visual-bell-active');
+    //   }, 200);
+    // }
   }
 
   /**
@@ -1141,7 +1136,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
       // Don't clear if it's already clear
       return;
     }
-    this.buffer.lines.set(0, this.buffer.lines.get(this.buffer.ybase + this.buffer.y));
+    this.buffer.lines.set(0, this.buffer.lines.get(this.buffer.ybase + this.buffer.y)!);
     this.buffer.lines.length = 1;
     this.buffer.ydisp = 0;
     this.buffer.ybase = 0;
@@ -1202,7 +1197,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
   }
 
   // TODO: Remove cancel function and cancelEvents option
-  public cancel(ev: Event, force?: boolean): boolean {
+  public cancel(ev: Event, force?: boolean): boolean | undefined {
     if (!this.options.cancelEvents && !force) {
       return;
     }
diff --git a/src/browser/Types.d.ts b/src/browser/Types.d.ts
index 847d64e5..76aa0c8c 100644
--- a/src/browser/Types.d.ts
+++ b/src/browser/Types.d.ts
@@ -8,14 +8,15 @@ import { IEvent } from 'common/EventEmitter';
 import { ICoreTerminal, CharData, ITerminalOptions } from 'common/Types';
 import { IMouseService, IRenderService } from './services/Services';
 import { IBuffer, IBufferSet } from 'common/buffer/Types';
+import { IFunctionIdentifier, IParams } from 'common/parser/Types';
 
 export interface ITerminal extends IPublicTerminal, ICoreTerminal {
   element: HTMLElement | undefined;
-  screenElement: HTMLElement;
+  screenElement: HTMLElement | undefined;
   browser: IBrowser;
   buffer: IBuffer;
   buffers: IBufferSet;
-  viewport: IViewport;
+  viewport: IViewport | undefined;
   // TODO: We should remove options once components adopt optionsService
   options: ITerminalOptions;
   linkifier: ILinkifier;
@@ -51,16 +52,16 @@ export interface IPublicTerminal extends IDisposable {
   resize(columns: number, rows: number): void;
   open(parent: HTMLElement): void;
   attachCustomKeyEventHandler(customKeyEventHandler: (event: KeyboardEvent) => boolean): void;
-  // addCsiHandler(id: IFunctionIdentifier, callback: (params: IParams) => boolean): IDisposable;
-  // addDcsHandler(id: IFunctionIdentifier, callback: (data: string, param: IParams) => boolean): IDisposable;
-  // addEscHandler(id: IFunctionIdentifier, callback: () => boolean): IDisposable;
-  // addOscHandler(ident: number, callback: (data: string) => boolean): IDisposable;
+  addCsiHandler(id: IFunctionIdentifier, callback: (params: IParams) => boolean): IDisposable;
+  addDcsHandler(id: IFunctionIdentifier, callback: (data: string, param: IParams) => boolean): IDisposable;
+  addEscHandler(id: IFunctionIdentifier, callback: () => boolean): IDisposable;
+  addOscHandler(ident: number, callback: (data: string) => boolean): IDisposable;
   registerLinkMatcher(regex: RegExp, handler: (event: MouseEvent, uri: string) => void, options?: ILinkMatcherOptions): number;
   deregisterLinkMatcher(matcherId: number): void;
   registerLinkProvider(linkProvider: ILinkProvider): IDisposable;
   registerCharacterJoiner(handler: (text: string) => [number, number][]): number;
   deregisterCharacterJoiner(joinerId: number): void;
-  addMarker(cursorYOffset: number): IMarker;
+  addMarker(cursorYOffset: number): IMarker | undefined;
   hasSelection(): boolean;
   getSelection(): string;
   getSelectionPosition(): ISelectionPosition | undefined;
diff --git a/src/browser/services/RenderService.ts b/src/browser/services/RenderService.ts
index a0ca25d2..d6b30524 100644
--- a/src/browser/services/RenderService.ts
+++ b/src/browser/services/RenderService.ts
@@ -10,7 +10,7 @@ import { Disposable } from 'common/Lifecycle';
 import { ScreenDprMonitor } from 'browser/ScreenDprMonitor';
 import { addDisposableDomListener } from 'browser/Lifecycle';
 import { IColorSet } from 'browser/Types';
-import { IOptionsService, IBufferService, ICoreService } from 'common/services/Services';
+import { IOptionsService, IBufferService } from 'common/services/Services';
 import { ICharSizeService, IRenderService } from 'browser/services/Services';
 
 interface ISelectionState {
diff --git a/src/public/Terminal.ts b/src/public/Terminal.ts
index d9b951ef..3d483814 100644
--- a/src/public/Terminal.ts
+++ b/src/public/Terminal.ts
@@ -4,7 +4,7 @@
  */
 
 import { Terminal as ITerminalApi, ITerminalOptions, IMarker, IDisposable, ILinkMatcherOptions, ITheme, ILocalizableStrings, ITerminalAddon, ISelectionPosition, IBuffer as IBufferApi, IBufferNamespace as IBufferNamespaceApi, IBufferLine as IBufferLineApi, IBufferCell as IBufferCellApi, IParser, IFunctionIdentifier, ILinkProvider, IUnicodeHandling, IUnicodeVersionProvider } from 'xterm';
-import { ITerminal } from '../Types';
+import { ITerminal } from 'browser/Types';
 import { IBufferLine, ICellData } from 'common/Types';
 import { IBuffer, IBufferSet } from 'common/buffer/Types';
 import { CellData } from 'common/buffer/CellData';
diff --git a/test/benchmark/Terminal.benchmark.ts b/test/benchmark/Terminal.benchmark.ts
index 71a36cc7..76139cb6 100644
--- a/test/benchmark/Terminal.benchmark.ts
+++ b/test/benchmark/Terminal.benchmark.ts
@@ -7,7 +7,7 @@ import { perfContext, before, ThroughputRuntimeCase } from 'xterm-benchmark';
 
 import { spawn } from 'node-pty';
 import { Utf8ToUtf32, stringFromCodePoint } from 'common/input/TextDecoder';
-import { Terminal } from 'Terminal';
+import { Terminal } from 'browser/Terminal';
 
 perfContext('Terminal: ls -lR /usr/lib', () => {
   let content = '';
diff --git a/typings/xterm.d.ts b/typings/xterm.d.ts
index 3487c410..35f43b1b 100644
--- a/typings/xterm.d.ts
+++ b/typings/xterm.d.ts
@@ -805,7 +805,7 @@ declare module 'xterm' {
     /**
      * @deprecated use `registerMarker` instead.
      */
-    addMarker(cursorYOffset: number): IMarker;
+    addMarker(cursorYOffset: number): IMarker | undefined;
 
     /**
      * Gets whether the terminal has an active selection.