use monotonic clock for elapsed time

src/js/component.js

@@ -1128,7 +1128,7 @@ class Component {
           pageY: event.touches[0].pageY
         };
         // Record start time so we can detect a tap vs. "touch and hold"
-        touchStart = new Date().getTime();
+        touchStart = window.performance.now();
         // Reset couldBeTap tracking
         couldBeTap = true;
       }
@@ -1166,7 +1166,7 @@ class Component {
       // Proceed only if the touchmove/leave/cancel event didn't happen
       if (couldBeTap === true) {
         // Measure how long the touch lasted
-        const touchTime = new Date().getTime() - touchStart;
+        const touchTime = window.performance.now() - touchStart;
 
         // Make sure the touch was less than the threshold to be considered a tap
         if (touchTime < touchTimeThreshold) {

src/js/utils/dom-data.js

@@ -3,6 +3,7 @@
  * @module dom-data
  */
 import * as Guid from './guid.js';
+import window from 'global/window';
 
 /**
  * Element Data Store.
@@ -23,7 +24,7 @@ const elData = {};
  * @constant
  * @private
  */
-const elIdAttr = 'vdata' + (new Date()).getTime();
+const elIdAttr = 'vdata' + Math.floor(window.performance && window.performance.now() || Date.now());
 
 /**
  * Returns the cache object where data for an element is stored

src/js/utils/fn.js

@@ -61,10 +61,10 @@ export const bind = function(context, fn, uid) {
  * @return   {Function}
  */
 export const throttle = function(fn, wait) {
-  let last = Date.now();
+  let last = window.performance.now();
 
   const throttled = function(...args) {
-    const now = Date.now();
+    const now = window.performance.now();
 
     if (now - last >= wait) {
       fn(...args);

test/unit/utils/fn.test.js

@@ -1,5 +1,6 @@
 /* eslint-env qunit */
 import sinon from 'sinon';
+import window from 'global/window';
 import * as Fn from '../../../src/js/utils/fn.js';
 
 QUnit.module('fn', {
@@ -22,6 +23,10 @@ QUnit.test('should add context to a function', function(assert) {
 });
 
 QUnit.test('should throttle functions properly', function(assert) {
+  // stub performance.now for sinon, see:
+  // https://github.com/sinonjs/sinon/issues/803
+  sinon.stub(window.performance, 'now', Date.now);
+
   const tester = sinon.spy();
   const throttled = Fn.throttle(tester, 100);