diff --git a/src/animation.js b/src/animation.js
index e9f6482..0d22978 100644
--- a/src/animation.js
+++ b/src/animation.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, scope, testing) {
 
   shared.sequenceNumber = 0;
@@ -191,7 +192,6 @@
       this._inEffect = false;
       this._idle = true;
       this._paused = false;
-      this._isFinished = true;
       this._finishedFlag = true;
       this._currentTime = 0;
       this._startTime = null;
diff --git a/src/apply-preserving-inline-style.js b/src/apply-preserving-inline-style.js
index 795be36..020ccf0 100644
--- a/src/apply-preserving-inline-style.js
+++ b/src/apply-preserving-inline-style.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   var styleAttributes = {
diff --git a/src/apply.js b/src/apply.js
index 3200f96..3d8c33e 100644
--- a/src/apply.js
+++ b/src/apply.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   scope.apply = function(element, property, value) {
diff --git a/src/box-handler.js b/src/box-handler.js
index 3399263..456cef0 100644
--- a/src/box-handler.js
+++ b/src/box-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
   function consumeLengthPercentOrAuto(string) {
     return scope.consumeLengthOrPercent(string) || scope.consumeToken(/^auto/, string);
diff --git a/src/color-handler.js b/src/color-handler.js
index b32a889..c5d96ce 100644
--- a/src/color-handler.js
+++ b/src/color-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   var canvas = document.createElementNS('http://www.w3.org/1999/xhtml', 'canvas');
diff --git a/src/deprecation.js b/src/deprecation.js
index 6bdb4a2..48fa2c8 100644
--- a/src/deprecation.js
+++ b/src/deprecation.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared) {
 
   var silenced = {};
diff --git a/src/dev.js b/src/dev.js
index a5e225c..640d0ad 100644
--- a/src/dev.js
+++ b/src/dev.js
@@ -12,5 +12,6 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 var WEB_ANIMATIONS_TESTING = false;
 var webAnimationsTesting = null;
diff --git a/src/dimension-handler.js b/src/dimension-handler.js
index 15e4d0a..78a1330 100644
--- a/src/dimension-handler.js
+++ b/src/dimension-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   function parseDimension(unitRegExp, string) {
diff --git a/src/effect-callback.js b/src/effect-callback.js
index 3051a59..29b5954 100644
--- a/src/effect-callback.js
+++ b/src/effect-callback.js
@@ -11,6 +11,8 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 //     See the License for the specific language governing permissions and
 // limitations under the License.
+
+'use strict';
 (function(shared, scope, testing) {
 
   var nullTarget = document.createElementNS('http://www.w3.org/1999/xhtml', 'div');
diff --git a/src/element-animatable.js b/src/element-animatable.js
index 765edf0..2b274c2 100644
--- a/src/element-animatable.js
+++ b/src/element-animatable.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope) {
   window.Element.prototype.animate = function(effectInput, options) {
     var id = '';
diff --git a/src/font-weight-handler.js b/src/font-weight-handler.js
index 4760486..1dc50bf 100644
--- a/src/font-weight-handler.js
+++ b/src/font-weight-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope) {
   function parse(string) {
     var out = Number(string);
diff --git a/src/group-constructors.js b/src/group-constructors.js
index e5c0a10..446db40 100644
--- a/src/group-constructors.js
+++ b/src/group-constructors.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, scope, testing) {
 
   function groupChildDuration(node) {
@@ -116,7 +117,8 @@
     },
     remove: function() {
       scope.removeMulti([this]);
-    }
+    },
+    _updateActiveDuration: function() {}
   };
 
   window.SequenceEffect.prototype = Object.create(constructor.prototype);
diff --git a/src/handler-utils.js b/src/handler-utils.js
index d9f05e1..be71c87 100644
--- a/src/handler-utils.js
+++ b/src/handler-utils.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope) {
 
   // consume* functions return a 2 value array of [parsed-data, '' or not-yet consumed input]
diff --git a/src/interpolation.js b/src/interpolation.js
index ba63ed3..c1a2c33 100644
--- a/src/interpolation.js
+++ b/src/interpolation.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   function interpolate(from, to, f) {
diff --git a/src/keyframe-effect-constructor.js b/src/keyframe-effect-constructor.js
index 3d0f1bd..13eb2ec 100644
--- a/src/keyframe-effect-constructor.js
+++ b/src/keyframe-effect-constructor.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, scope, testing) {
 
   var disassociate = function(effect) {
@@ -70,7 +71,7 @@
       this._normalizedKeyframes = new KeyframeList(effectInput);
     }
     this._keyframes = effectInput;
-    this.activeDuration = shared.calculateActiveDuration(this._timing);
+    this._updateActiveDuration();
     this._id = id;
     return this;
   };
@@ -93,6 +94,9 @@
     get parent() {
       return this._parent;
     },
+    get activeDuration() {
+      return this._activeDuration;
+    },
     clone: function() {
       if (typeof this.getFrames() == 'function') {
         throw new Error('Cloning custom effects is not supported.');
@@ -104,6 +108,9 @@
     },
     remove: function() {
       scope.removeMulti([this]);
+    },
+    _updateActiveDuration: function() {
+      this._activeDuration = shared.calculateActiveDuration(this._timing);
     }
   };
 
diff --git a/src/keyframe-effect.js b/src/keyframe-effect.js
index f6813d8..c69b9ad 100644
--- a/src/keyframe-effect.js
+++ b/src/keyframe-effect.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, scope, testing) {
 
   function EffectTime(timing) {
diff --git a/src/keyframe-interpolations.js b/src/keyframe-interpolations.js
index cab801e..f57d6b4 100644
--- a/src/keyframe-interpolations.js
+++ b/src/keyframe-interpolations.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, scope, testing) {
 
   scope.convertEffectInput = function(effectInput) {
diff --git a/src/matrix-decomposition.js b/src/matrix-decomposition.js
index 357df9c..57e787b 100644
--- a/src/matrix-decomposition.js
+++ b/src/matrix-decomposition.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
   var decomposeMatrix = (function() {
     function determinant(m) {
diff --git a/src/matrix-interpolation.js b/src/matrix-interpolation.js
index 9a35de3..c19dde5 100644
--- a/src/matrix-interpolation.js
+++ b/src/matrix-interpolation.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
   var composeMatrix = (function() {
     function multiply(a, b) {
diff --git a/src/normalize-keyframes.js b/src/normalize-keyframes.js
index 1fd0254..6137c84 100644
--- a/src/normalize-keyframes.js
+++ b/src/normalize-keyframes.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, testing) {
   var shorthandToLonghand = {
     background: [
diff --git a/src/number-handler.js b/src/number-handler.js
index 7509373..95ae461 100644
--- a/src/number-handler.js
+++ b/src/number-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   function numberToString(x) {
diff --git a/src/position-handler.js b/src/position-handler.js
index 18cea43..32b9593 100644
--- a/src/position-handler.js
+++ b/src/position-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope) {
 
   function negateDimension(dimension) {
diff --git a/src/property-interpolation.js b/src/property-interpolation.js
index 2e2c5e0..4005507 100644
--- a/src/property-interpolation.js
+++ b/src/property-interpolation.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, scope, testing) {
 
   var propertyHandlers = {};
diff --git a/src/property-names.js b/src/property-names.js
index c52d990..557fccd 100644
--- a/src/property-names.js
+++ b/src/property-names.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   var aliased = {};
diff --git a/src/scope.js b/src/scope.js
index c824880..9bab6b6 100644
--- a/src/scope.js
+++ b/src/scope.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 var webAnimationsShared = {};
 var webAnimations1 = {};
 var webAnimationsNext = {};
diff --git a/src/shadow-handler.js b/src/shadow-handler.js
index 3f8201d..531b1b9 100644
--- a/src/shadow-handler.js
+++ b/src/shadow-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope) {
 
   function consumeShadow(string) {
diff --git a/src/shape-handler.js b/src/shape-handler.js
index 6bbf79f..1ad5048 100644
--- a/src/shape-handler.js
+++ b/src/shape-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope) {
 
   var consumeLengthOrPercent = scope.consumeParenthesised.bind(null, scope.parseLengthOrPercent);
diff --git a/src/tick.js b/src/tick.js
index 08b0a14..6d8f7ac 100644
--- a/src/tick.js
+++ b/src/tick.js
@@ -12,7 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
-
+'use strict';
 (function(shared, scope, testing) {
   var originalRequestAnimationFrame = window.requestAnimationFrame;
   var rafCallbacks = [];
diff --git a/src/timeline.js b/src/timeline.js
index 2b213b5..605a54d 100644
--- a/src/timeline.js
+++ b/src/timeline.js
@@ -12,7 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
-
+'use strict';
 (function(shared, scope, testing) {
   var originalRequestAnimationFrame = window.requestAnimationFrame;
   window.requestAnimationFrame = function(f) {
diff --git a/src/timing-utilities.js b/src/timing-utilities.js
index 2f16f3b..ffbe008 100644
--- a/src/timing-utilities.js
+++ b/src/timing-utilities.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, testing) {
 
   var fills = 'backwards|forwards|both|none'.split('|');
@@ -52,7 +53,7 @@
       if (this._effect) {
         this._effect._timingInput[member] = value;
         this._effect._timing = shared.normalizeTimingInput(this._effect._timingInput);
-        this._effect.activeDuration = shared.calculateActiveDuration(this._effect._timing);
+        this._effect._updateActiveDuration();
         if (this._effect._animation) {
           this._effect._animation._rebuildUnderlyingAnimation();
         }
@@ -143,7 +144,7 @@
           if ((property == 'direction') && (directions.indexOf(timingInput[property]) == -1)) {
             return;
           }
-          if (property == 'playbackRate' && timingInput[property] !== 1 && shared.isDeprecated('AnimationEffectTiming.playbackRate', '2014-11-28', 'Use Animation.playbackRate instead.')) {
+          if (property == 'playbackRate') {
             return;
           }
           timing[property] = timingInput[property];
diff --git a/src/transform-handler.js b/src/transform-handler.js
index c448296..ad227f5 100644
--- a/src/transform-handler.js
+++ b/src/transform-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   // This returns a function for converting transform functions to equivalent
diff --git a/src/visibility-handler.js b/src/visibility-handler.js
index 53f2953..31e8d77 100644
--- a/src/visibility-handler.js
+++ b/src/visibility-handler.js
@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(scope, testing) {
 
   function merge(left, right) {
diff --git a/src/web-animations-bonus-cancel-events.js b/src/web-animations-bonus-cancel-events.js
index 3905496..2e9cf1f 100644
--- a/src/web-animations-bonus-cancel-events.js
+++ b/src/web-animations-bonus-cancel-events.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function() {
 
   if (document.createElement('div').animate([]).oncancel !== undefined) {
diff --git a/src/web-animations-bonus-object-form-keyframes.js b/src/web-animations-bonus-object-form-keyframes.js
index c1b6ecd..8aeebcb 100644
--- a/src/web-animations-bonus-object-form-keyframes.js
+++ b/src/web-animations-bonus-object-form-keyframes.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared) {
   // If the polyfill is being loaded in a context where Element.animate is
   // supported but object-form syntax is not, then creating an animation
diff --git a/src/web-animations-next-animation.js b/src/web-animations-next-animation.js
index 698532c..4738694 100644
--- a/src/web-animations-next-animation.js
+++ b/src/web-animations-next-animation.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function(shared, scope, testing) {
   scope.animationsWithPromises = [];
 
diff --git a/test/testharness-runner.js b/test/testharness-runner.js
index 1a9a909..71e9ddb 100644
--- a/test/testharness-runner.js
+++ b/test/testharness-runner.js
@@ -12,6 +12,7 @@
 //     See the License for the specific language governing permissions and
 // limitations under the License.
 
+'use strict';
 (function() {
   var assert = chai.assert;
   mocha.setup({ ui: 'tdd' });