Make doubley sure Date.now, clearTimeout, and setTimeout are mockable.

lodash.js

@@ -1282,7 +1282,6 @@
 
     /** Built-in constructor references. */
     var Array = context.Array,
-        Date = context.Date,
         Error = context.Error,
         Math = context.Math,
         RegExp = context.RegExp,
@@ -1342,9 +1341,10 @@
         splice = arrayProto.splice,
         spreadableSymbol = Symbol ? Symbol.isConcatSpreadable : undefined;
 
-    /** Built-in method references that are mockable. */
-    var clearTimeout = function(id) { return context.clearTimeout.call(root, id); },
-        setTimeout = function(func, wait) { return context.setTimeout.call(root, func, wait); };
+    /** Mocked built-ins. */
+    var ctxClearTimeout = context.clearTimeout !== root.clearTimeout && context.clearTimeout,
+        ctxNow = context.Date && context.Date.now !== root.Date.now && context.Date.now,
+        ctxSetTimeout = context.setTimeout !== root.setTimeout && context.setTimeout;
 
     /* Built-in method references for those with the same name as other `lodash` methods. */
     var nativeCeil = Math.ceil,
@@ -4157,6 +4157,16 @@
       return (!start && end >= length) ? array : baseSlice(array, start, end);
     }
 
+    /**
+     * A simple wrapper around the global [`clearTimeout`](https://mdn.io/clearTimeout).
+     *
+     * @private
+     * @param {number} id The id of the timer to clear.
+     */
+    var clearTimeout = ctxClearTimeout || function(id) {
+      return root.clearTimeout(id);
+    };
+
     /**
      * Creates a clone of  `buffer`.
      *
@@ -6187,6 +6197,18 @@
       };
     }());
 
+    /**
+     * A simple wrapper around the global [`setTimeout`](https://mdn.io/setTimeout).
+     *
+     * @private
+     * @param {Function} func The function to delay.
+     * @param {number} wait The number of milliseconds to delay invocation.
+     * @returns {number} Returns the timer id.
+     */
+    var setTimeout = ctxSetTimeout || function(func, wait) {
+      return root.setTimeout(func, wait);
+    };
+
     /**
      * Sets the `toString` method of `wrapper` to mimic the source of `reference`
      * with wrapper details in a comment at the top of the source body.
@@ -9487,9 +9509,9 @@
      * }, _.now());
      * // => Logs the number of milliseconds it took for the deferred invocation.
      */
-    function now() {
-      return Date.now();
-    }
+    var now = ctxNow || function() {
+      return root.Date.now();
+    };
 
     /*------------------------------------------------------------------------*/