diff --git a/src/Interfaces.ts b/src/Interfaces.ts
new file mode 100644
index 00000000..14355e57
--- /dev/null
+++ b/src/Interfaces.ts
@@ -0,0 +1,14 @@
+/**
+ * xterm.js: xterm, in the browser
+ * Copyright (c) 2014-2016, SourceLair Private Company (www.sourcelair.com (MIT License)
+ */
+
+export interface ITerminal {
+  rowContainer: HTMLElement;
+  ydisp: number;
+  lines: string[];
+  rows: number;
+
+  on(event: string, callback: () => void);
+  scrollDisp(disp: number, suppressScrollEvent: boolean);
+}
diff --git a/src/Viewport.ts b/src/Viewport.ts
index b47e8053..573a050c 100644
--- a/src/Viewport.ts
+++ b/src/Viewport.ts
@@ -3,112 +3,119 @@
  * Copyright (c) 2014-2016, SourceLair Private Company (www.sourcelair.com (MIT License)
  */
 
+import { ITerminal } from './Interfaces';
+
 /**
  * Represents the viewport of a terminal, the visible area within the larger buffer of output.
  * Logic for the virtual scroll bar is included in this object.
- * @param {Terminal} terminal The Terminal object.
- * @param {HTMLElement} viewportElement The DOM element acting as the viewport
- * @param {HTMLElement} charMeasureElement A DOM element used to measure the character size of
- *   the terminal.
+ * @param viewportElement The DOM element acting as the viewport.
+ * @param scrollArea The DOM element acting as the scroll area.
+ * @param charMeasureElement A DOM element used to measure the character size of. the terminal.
  */
-function Viewport(terminal, viewportElement, scrollArea, charMeasureElement) {
-  this.terminal = terminal;
-  this.viewportElement = viewportElement;
-  this.scrollArea = scrollArea;
-  this.charMeasureElement = charMeasureElement;
-  this.currentRowHeight = 0;
-  this.lastRecordedBufferLength = 0;
-  this.lastRecordedViewportHeight = 0;
+export class Viewport {
 
-  this.terminal.on('scroll', this.syncScrollArea.bind(this));
-  this.terminal.on('resize', this.syncScrollArea.bind(this));
-  this.viewportElement.addEventListener('scroll', this.onScroll.bind(this));
+  private currentRowHeight: number;
+  private lastRecordedBufferLength: number;
+  private lastRecordedViewportHeight: number;
 
-  this.syncScrollArea();
+  constructor(
+    private terminal: ITerminal,
+    private viewportElement: HTMLElement,
+    private scrollArea: HTMLElement,
+    private charMeasureElement: HTMLElement
+  ) {
+    this.currentRowHeight = 0;
+    this.lastRecordedBufferLength = 0;
+    this.lastRecordedViewportHeight = 0;
+
+    this.terminal.on('scroll', this.syncScrollArea.bind(this));
+    this.terminal.on('resize', this.syncScrollArea.bind(this));
+    this.viewportElement.addEventListener('scroll', this.onScroll.bind(this));
+
+    this.syncScrollArea();
+  }
+
+  /**
+   * Refreshes row height, setting line-height, viewport height and scroll area height if
+   * necessary.
+   * @param charSize A character size measurement bounding rect object, if it doesn't exist it will
+   *   be created.
+   */
+  private refresh(charSize?: ClientRect): void {
+    var size = charSize || this.charMeasureElement.getBoundingClientRect();
+    if (size.height > 0) {
+      var rowHeightChanged = size.height !== this.currentRowHeight;
+      if (rowHeightChanged) {
+        this.currentRowHeight = size.height;
+        this.viewportElement.style.lineHeight = size.height + 'px';
+        this.terminal.rowContainer.style.lineHeight = size.height + 'px';
+      }
+      var viewportHeightChanged = this.lastRecordedViewportHeight !== this.terminal.rows;
+      if (rowHeightChanged || viewportHeightChanged) {
+        this.lastRecordedViewportHeight = this.terminal.rows;
+        this.viewportElement.style.height = size.height * this.terminal.rows + 'px';
+      }
+      this.scrollArea.style.height = (size.height * this.lastRecordedBufferLength) + 'px';
+    }
+  }
+
+  /**
+   * Updates dimensions and synchronizes the scroll area if necessary.
+   */
+  public syncScrollArea(): void {
+    if (this.lastRecordedBufferLength !== this.terminal.lines.length) {
+      // If buffer height changed
+      this.lastRecordedBufferLength = this.terminal.lines.length;
+      this.refresh();
+    } else if (this.lastRecordedViewportHeight !== this.terminal.rows) {
+      // If viewport height changed
+      this.refresh();
+    } else {
+      // If size has changed, refresh viewport
+      var size = this.charMeasureElement.getBoundingClientRect();
+      if (size.height !== this.currentRowHeight) {
+        this.refresh(size);
+      }
+    }
+
+    // Sync scrollTop
+    var scrollTop = this.terminal.ydisp * this.currentRowHeight;
+    if (this.viewportElement.scrollTop !== scrollTop) {
+      this.viewportElement.scrollTop = scrollTop;
+    }
+  }
+
+  /**
+   * Handles scroll events on the viewport, calculating the new viewport and requesting the
+   * terminal to scroll to it.
+   * @param ev The scroll event.
+   */
+  private onScroll(ev: Event) {
+    var newRow = Math.round(this.viewportElement.scrollTop / this.currentRowHeight);
+    var diff = newRow - this.terminal.ydisp;
+    this.terminal.scrollDisp(diff, true);
+  }
+
+  /**
+   * Handles mouse wheel events by adjusting the viewport's scrollTop and delegating the actual
+   * scrolling to `onScroll`, this event needs to be attached manually by the consumer of
+   * `Viewport`.
+   * @param ev The mouse wheel event.
+   */
+  public onWheel(ev: WheelEvent) {
+    if (ev.deltaY === 0) {
+      // Do nothing if it's not a vertical scroll event
+      return;
+    }
+    // Fallback to WheelEvent.DOM_DELTA_PIXEL
+    var multiplier = 1;
+    if (ev.deltaMode === WheelEvent.DOM_DELTA_LINE) {
+      multiplier = this.currentRowHeight;
+    } else if (ev.deltaMode === WheelEvent.DOM_DELTA_PAGE) {
+      multiplier = this.currentRowHeight * this.terminal.rows;
+    }
+    this.viewportElement.scrollTop += ev.deltaY * multiplier;
+    // Prevent the page from scrolling when the terminal scrolls
+    ev.preventDefault();
+  };
 }
-
-/**
- * Refreshes row height, setting line-height, viewport height and scroll area height if
- * necessary.
- * @param {number|undefined} charSize A character size measurement bounding rect object, if it
- *   doesn't exist it will be created.
- */
-Viewport.prototype.refresh = function(charSize) {
-  var size = charSize || this.charMeasureElement.getBoundingClientRect();
-  if (size.height > 0) {
-    var rowHeightChanged = size.height !== this.currentRowHeight;
-    if (rowHeightChanged) {
-      this.currentRowHeight = size.height;
-      this.viewportElement.style.lineHeight = size.height + 'px';
-      this.terminal.rowContainer.style.lineHeight = size.height + 'px';
-    }
-    var viewportHeightChanged = this.lastRecordedViewportHeight !== this.terminal.rows;
-    if (rowHeightChanged || viewportHeightChanged) {
-      this.lastRecordedViewportHeight = this.terminal.rows;
-      this.viewportElement.style.height = size.height * this.terminal.rows + 'px';
-    }
-    this.scrollArea.style.height = (size.height * this.lastRecordedBufferLength) + 'px';
-  }
-};
-
-/**
- * Updates dimensions and synchronizes the scroll area if necessary.
- */
-Viewport.prototype.syncScrollArea = function() {
-  if (this.lastRecordedBufferLength !== this.terminal.lines.length) {
-    // If buffer height changed
-    this.lastRecordedBufferLength = this.terminal.lines.length;
-    this.refresh();
-  } else if (this.lastRecordedViewportHeight !== this.terminal.rows) {
-    // If viewport height changed
-    this.refresh();
-  } else {
-    // If size has changed, refresh viewport
-    var size = this.charMeasureElement.getBoundingClientRect();
-    if (size.height !== this.currentRowHeight) {
-      this.refresh(size);
-    }
-  }
-
-  // Sync scrollTop
-  var scrollTop = this.terminal.ydisp * this.currentRowHeight;
-  if (this.viewportElement.scrollTop !== scrollTop) {
-    this.viewportElement.scrollTop = scrollTop;
-  }
-};
-
-/**
- * Handles scroll events on the viewport, calculating the new viewport and requesting the
- * terminal to scroll to it.
- * @param {Event} ev The scroll event.
- */
-Viewport.prototype.onScroll = function(ev) {
-  var newRow = Math.round(this.viewportElement.scrollTop / this.currentRowHeight);
-  var diff = newRow - this.terminal.ydisp;
-  this.terminal.scrollDisp(diff, true);
-};
-
-/**
- * Handles mouse wheel events by adjusting the viewport's scrollTop and delegating the actual
- * scrolling to `onScroll`, this event needs to be attached manually by the consumer of
- * `Viewport`.
- * @param {WheelEvent} ev The mouse wheel event.
- */
-Viewport.prototype.onWheel = function(ev) {
-  if (ev.deltaY === 0) {
-    // Do nothing if it's not a vertical scroll event
-    return;
-  }
-  // Fallback to WheelEvent.DOM_DELTA_PIXEL
-  var multiplier = 1;
-  if (ev.deltaMode === WheelEvent.DOM_DELTA_LINE) {
-    multiplier = this.currentRowHeight;
-  } else if (ev.deltaMode === WheelEvent.DOM_DELTA_PAGE) {
-    multiplier = this.currentRowHeight * this.terminal.rows;
-  }
-  this.viewportElement.scrollTop += ev.deltaY * multiplier;
-  // Prevent the page from scrolling when the terminal scrolls
-  ev.preventDefault();
-};
-
-export { Viewport };