diff --git a/src/ol/deviceorientation.js b/src/ol/deviceorientation.js
index 2933d89a83..2b2d95f3fc 100644
--- a/src/ol/deviceorientation.js
+++ b/src/ol/deviceorientation.js
@@ -3,6 +3,7 @@ goog.provide('ol.DeviceOrientationProperty');
 
 goog.require('goog.events');
 goog.require('goog.math');
+goog.require('ol');
 goog.require('ol.Object');
 goog.require('ol.has');
 
@@ -79,7 +80,7 @@ ol.DeviceOrientation = function(opt_options) {
 
   goog.base(this);
 
-  var options = goog.isDef(opt_options) ? opt_options : {};
+  var options = opt_options ? opt_options : {};
 
   /**
    * @private
@@ -91,7 +92,8 @@ ol.DeviceOrientation = function(opt_options) {
       ol.Object.getChangeEventType(ol.DeviceOrientationProperty.TRACKING),
       this.handleTrackingChanged_, false, this);
 
-  this.setTracking(goog.isDef(options.tracking) ? options.tracking : false);
+  this.setTracking(ol.isDef(options.tracking) ?
+      /** @type {boolean} */ (options.tracking) : false);
 
 };
 goog.inherits(ol.DeviceOrientation, ol.Object);
diff --git a/src/ol/dom/dom.js b/src/ol/dom/dom.js
index d3ede697d7..86eb2b2b04 100644
--- a/src/ol/dom/dom.js
+++ b/src/ol/dom/dom.js
@@ -19,10 +19,10 @@ goog.require('ol');
  */
 ol.dom.createCanvasContext2D = function(opt_width, opt_height) {
   var canvas = goog.dom.createElement(goog.dom.TagName.CANVAS);
-  if (goog.isDef(opt_width)) {
+  if (opt_width) {
     canvas.width = opt_width;
   }
-  if (goog.isDef(opt_height)) {
+  if (opt_height) {
     canvas.height = opt_height;
   }
   return canvas.getContext('2d');
@@ -47,7 +47,7 @@ ol.dom.BrowserFeature = {
 ol.dom.canUseCssTransform = (function() {
   var canUseCssTransform;
   return function() {
-    if (!goog.isDef(canUseCssTransform)) {
+    if (!ol.isDef(canUseCssTransform)) {
       goog.asserts.assert(!goog.isNull(document.body),
           'document.body should not be null');
       if (!goog.global.getComputedStyle) {
@@ -90,7 +90,7 @@ ol.dom.canUseCssTransform = (function() {
 ol.dom.canUseCssTransform3D = (function() {
   var canUseCssTransform3D;
   return function() {
-    if (!goog.isDef(canUseCssTransform3D)) {
+    if (!ol.isDef(canUseCssTransform3D)) {
       goog.asserts.assert(!goog.isNull(document.body),
           'document.body should not be null');
       if (!goog.global.getComputedStyle) {
@@ -224,7 +224,7 @@ ol.dom.transformElement2D =
   if (ol.dom.canUseCssTransform3D()) {
     var value3D;
 
-    if (goog.isDef(opt_precision)) {
+    if (ol.isDef(opt_precision)) {
       /** @type {Array.<string>} */
       var strings3D = new Array(16);
       for (i = 0; i < 16; ++i) {
@@ -246,7 +246,7 @@ ol.dom.transformElement2D =
       goog.vec.Mat4.getElement(transform, 1, 3)
     ];
     var value2D;
-    if (goog.isDef(opt_precision)) {
+    if (ol.isDef(opt_precision)) {
       /** @type {Array.<string>} */
       var strings2D = new Array(6);
       for (i = 0; i < 6; ++i) {
diff --git a/src/ol/extent.js b/src/ol/extent.js
index 5c13604b5f..086f7e433d 100644
--- a/src/ol/extent.js
+++ b/src/ol/extent.js
@@ -87,7 +87,7 @@ ol.extent.boundingExtentXYs_ = function(xs, ys, opt_extent) {
  * @api stable
  */
 ol.extent.buffer = function(extent, value, opt_extent) {
-  if (goog.isDef(opt_extent)) {
+  if (opt_extent) {
     opt_extent[0] = extent[0] - value;
     opt_extent[1] = extent[1] - value;
     opt_extent[2] = extent[2] + value;
@@ -112,7 +112,7 @@ ol.extent.buffer = function(extent, value, opt_extent) {
  * @return {ol.Extent} The clone.
  */
 ol.extent.clone = function(extent, opt_extent) {
-  if (goog.isDef(opt_extent)) {
+  if (opt_extent) {
     opt_extent[0] = extent[0];
     opt_extent[1] = extent[1];
     opt_extent[2] = extent[2];
@@ -247,7 +247,7 @@ ol.extent.createEmpty = function() {
  * @return {ol.Extent} Extent.
  */
 ol.extent.createOrUpdate = function(minX, minY, maxX, maxY, opt_extent) {
-  if (goog.isDef(opt_extent)) {
+  if (opt_extent) {
     opt_extent[0] = minX;
     opt_extent[1] = minY;
     opt_extent[2] = maxX;
@@ -545,7 +545,7 @@ ol.extent.getCorner = function(extent, corner) {
   } else {
     goog.asserts.fail('Invalid corner: %s', corner);
   }
-  goog.asserts.assert(goog.isDef(coordinate), 'coordinate should be defined');
+  goog.asserts.assert(coordinate, 'coordinate should be defined');
   return coordinate;
 };
 
@@ -624,8 +624,7 @@ ol.extent.getIntersectionArea = function(extent1, extent2) {
  * @api stable
  */
 ol.extent.getIntersection = function(extent1, extent2, opt_extent) {
-  var intersection = goog.isDef(opt_extent) ?
-      opt_extent : ol.extent.createEmpty();
+  var intersection = opt_extent ? opt_extent : ol.extent.createEmpty();
   if (ol.extent.intersects(extent1, extent2)) {
     if (extent1[0] > extent2[0]) {
       intersection[0] = extent1[0];
@@ -760,7 +759,7 @@ ol.extent.normalize = function(extent, coordinate) {
  * @return {ol.Extent} Extent.
  */
 ol.extent.returnOrUpdate = function(extent, opt_extent) {
-  if (goog.isDef(opt_extent)) {
+  if (opt_extent) {
     opt_extent[0] = extent[0];
     opt_extent[1] = extent[1];
     opt_extent[2] = extent[2];
@@ -886,7 +885,7 @@ ol.extent.applyTransform = function(extent, transformFn, opt_extent) {
  * @return {ol.Extent} The transformed extent.
  */
 ol.extent.transform2D = function(extent, transform, opt_extent) {
-  var dest = goog.isDef(opt_extent) ? opt_extent : [];
+  var dest = opt_extent ? opt_extent : [];
   var m00 = goog.vec.Mat4.getElement(transform, 0, 0);
   var m10 = goog.vec.Mat4.getElement(transform, 1, 0);
   var m01 = goog.vec.Mat4.getElement(transform, 0, 1);
diff --git a/src/ol/feature.js b/src/ol/feature.js
index 126edf8805..d3ca941779 100644
--- a/src/ol/feature.js
+++ b/src/ol/feature.js
@@ -5,6 +5,7 @@ goog.require('goog.asserts');
 goog.require('goog.events');
 goog.require('goog.events.EventType');
 goog.require('goog.functions');
+goog.require('ol');
 goog.require('ol.Object');
 goog.require('ol.geom.Geometry');
 goog.require('ol.style.Style');
@@ -96,7 +97,7 @@ ol.Feature = function(opt_geometryOrProperties) {
       this, ol.Object.getChangeEventType(this.geometryName_),
       this.handleGeometryChanged_, false, this);
 
-  if (goog.isDef(opt_geometryOrProperties)) {
+  if (ol.isDef(opt_geometryOrProperties)) {
     if (opt_geometryOrProperties instanceof ol.geom.Geometry ||
         goog.isNull(opt_geometryOrProperties)) {
       var geometry = /** @type {ol.geom.Geometry} */ (opt_geometryOrProperties);