Remove var usage from Viewport

Part of #335

src/Viewport.ts

@@ -46,13 +46,13 @@ export class Viewport {
   private refresh(charSize?: ClientRect): void {
     var size = charSize || this.charMeasureElement.getBoundingClientRect();
     if (size.height > 0) {
-      var rowHeightChanged = size.height !== this.currentRowHeight;
+      const 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;
+      const viewportHeightChanged = this.lastRecordedViewportHeight !== this.terminal.rows;
       if (rowHeightChanged || viewportHeightChanged) {
         this.lastRecordedViewportHeight = this.terminal.rows;
         this.viewportElement.style.height = size.height * this.terminal.rows + 'px';
@@ -74,14 +74,14 @@ export class Viewport {
       this.refresh();
     } else {
       // If size has changed, refresh viewport
-      var size = this.charMeasureElement.getBoundingClientRect();
+      const size = this.charMeasureElement.getBoundingClientRect();
       if (size.height !== this.currentRowHeight) {
         this.refresh(size);
       }
     }
 
     // Sync scrollTop
-    var scrollTop = this.terminal.ydisp * this.currentRowHeight;
+    const scrollTop = this.terminal.ydisp * this.currentRowHeight;
     if (this.viewportElement.scrollTop !== scrollTop) {
       this.viewportElement.scrollTop = scrollTop;
     }
@@ -93,8 +93,8 @@ export class Viewport {
    * @param ev The scroll event.
    */
   private onScroll(ev: Event) {
-    var newRow = Math.round(this.viewportElement.scrollTop / this.currentRowHeight);
+    const newRow = Math.round(this.viewportElement.scrollTop / this.currentRowHeight);
-    var diff = newRow - this.terminal.ydisp;
+    const diff = newRow - this.terminal.ydisp;
     this.terminal.scrollDisp(diff, true);
   }
 
@@ -110,7 +110,7 @@ export class Viewport {
       return;
     }
     // Fallback to WheelEvent.DOM_DELTA_PIXEL
-    var multiplier = 1;
+    let multiplier = 1;
     if (ev.deltaMode === WheelEvent.DOM_DELTA_LINE) {
       multiplier = this.currentRowHeight;
     } else if (ev.deltaMode === WheelEvent.DOM_DELTA_PAGE) {