Ensure checks based Object.keys length pass for fake Dates

src/fake-timers-src.js

@@ -22,10 +22,10 @@
  */
 
 /**
  * Queues a function to be called during a browser's idle periods
  *
  * @callback RequestIdleCallback
  * @param {function(IdleDeadline)} callback
  * @param {{timeout: number}} options - an options object
  * @returns {number} the id
  */
@@ -52,13 +52,13 @@
 
 /**
  * @typedef RequestAnimationFrame
  * @property {function(number):void} requestAnimationFrame
  * @returns {number} - the id
  */
 
 /**
  * @typedef Performance
  * @property {function(): number} now
  */
 
 /* eslint-disable jsdoc/require-property-description */
@@ -105,7 +105,7 @@
 /* eslint-enable jsdoc/require-property-description */
 
 /**
  * Configuration object for the `install` method.
  *
  * @typedef {object} Config
  * @property {number|Date} [now] a number (in milliseconds) or a Date object (default epoch)
@@ -119,7 +119,7 @@
 
 /* eslint-disable jsdoc/require-property-description */
 /**
  * The internal structure to describe a scheduled fake timer
  *
  * @typedef {object} Timer
  * @property {Function} func
@@ -133,7 +133,7 @@
  */
 
 /**
  * A Node timer
  *
  * @typedef {object} NodeImmediate
  * @property {function(): boolean} hasRef
@@ -145,7 +145,7 @@
 /* eslint-disable complexity */
 
 /**
  * Mocks available features in the specified global namespace.
  *
  * @param {*} _global Namespace to mock (e.g. `window`)
  * @returns {FakeTimers}
@@ -275,7 +275,7 @@
     /**
      * Parse strings like "01:10:00" (meaning 1 hour, 10 minutes, 0 seconds) into
      * number of milliseconds. This is used to support human-readable strings passed
      * to clock.tick()
      *
      * @param {string} str
      * @returns {number}
@@ -311,7 +311,7 @@
     }
 
     /**
      * Get the decimal part of the millisecond value as nanoseconds
      *
      * @param {number} msFloat the number of milliseconds
      * @returns {number} an integer number of nanoseconds in the range [0,1e6)
@@ -450,7 +450,10 @@
 
                 // ensures identity checks using the constructor prop still works
                 // this should have no other functional effect
-                this.constructor = NativeDate;
+                Object.defineProperty(this, "constructor", {
+                    value: NativeDate,
+                    enumerable: false,
+                });
             }
 
             static [Symbol.hasInstance](instance) {

test/fake-timers-test.js

@@ -3212,6 +3212,12 @@ describe("FakeTimers", function () {
             assert.equals(date.constructor, realDate.constructor);
         });
 
+        it("creates Date objects where the constructor prop is not enumerable", function () {
+            const date = new this.clock.Date();
+
+            assert.equals(Object.keys(date).length, 0);
+        });
+
         it("creates Date objects representing clock time", function () {
             const date = new this.clock.Date();