--- a/testing/web-platform/tests/resources/idlharness.js
+++ b/testing/web-platform/tests/resources/idlharness.js
@@ -1598,25 +1598,20 @@ IdlInterface.prototype.test = function()
     // members might themselves be marked as .untested.  This might happen to
     // interfaces if the interface itself is untested but a partial interface
     // that extends it is tested -- then the interface itself and its initial
     // members will be marked as untested, but the members added by the partial
     // interface are still tested.
     this.test_members();
 };
 
-// This supports both Constructor extended attributes and constructor
-// operations until all idl fragments have been updated.
 IdlInterface.prototype.constructors = function()
 {
-    var extendedAttributes = this.extAttrs
-        .filter(function(attr) { return attr.name == "Constructor"; });
-    var operations = this.members
+    return this.members
         .filter(function(m) { return m.type == "constructor"; });
-    return extendedAttributes.concat(operations);
 }
 
 IdlInterface.prototype.test_self = function()
 {
     subsetTestByKey(this.name, test, function()
     {
         // This function tests WebIDL as of 2015-01-13.
 
@@ -1691,21 +1686,17 @@ IdlInterface.prototype.test_self = funct
             // "If the interface doesn't inherit from any other interface, the
             // value of [[Prototype]] is %FunctionPrototype% ([ECMA-262],
             // section 6.1.7.4)."
             assert_equals(prototype, Function.prototype,
                           "prototype of self's property " + format_value(this.name) + " is not Function.prototype");
         }
 
         if (!this.constructors().length) {
-            // "The internal [[Call]] method of the interface object behaves as
-            // follows . . .
-            //
-            // "If I was not declared with a [Constructor] extended attribute,
-            // then throw a TypeError."
+            // "If I was not declared with a constructor operation, then throw a TypeError."
             var interface_object = this.get_interface_object();
             assert_throws_js(globalOf(interface_object).TypeError, function() {
                 interface_object();
             }, "interface object didn't throw TypeError when called as a function");
             assert_throws_js(globalOf(interface_object).TypeError, function() {
                 new interface_object();
             }, "interface object didn't throw TypeError when called as a constructor");
         }

--- a/testing/web-platform/tests/resources/test/tests/functional/idlharness/IdlInterface/test_immutable_prototype.html
+++ b/testing/web-platform/tests/resources/test/tests/functional/idlharness/IdlInterface/test_immutable_prototype.html
@@ -28,18 +28,18 @@ Object.defineProperty(window.Foo, "proto
 Foo.prototype[Symbol.toStringTag] = "Foo";
 
 var idlArray = new IdlArray();
 idlArray.add_untested_idls("interface EventTarget {};");
 idlArray.add_idls(
     "[Global=Window, Exposed=Window]\n" +
     "interface Window : EventTarget {};\n" +
 
-    "[Global=Window, Exposed=Window, Constructor()]\n" +
-    "interface Foo {};"
+    "[Global=Window, Exposed=Window]\n" +
+    "interface Foo { constructor(); };"
   );
 idlArray.add_objects({
   Foo: ["new Foo()"],
   Window: ["window"]
 });
 idlArray.test();
 </script>
 <script type="text/json" id="expected">

--- a/testing/web-platform/tests/resources/test/tests/functional/idlharness/IdlInterface/test_primary_interface_of.html
+++ b/testing/web-platform/tests/resources/test/tests/functional/idlharness/IdlInterface/test_primary_interface_of.html
@@ -35,18 +35,17 @@ Object.defineProperty(window.Foo.prototy
     value: window.Foo
   });
 Object.setPrototypeOf(Foo, FooParent);
 Foo.prototype[Symbol.toStringTag] = "Foo";
 
 var idlArray = new IdlArray();
 idlArray.add_untested_idls("interface FooParent {};");
 idlArray.add_idls(
-    "[Constructor()]\n" +
-    "interface Foo : FooParent {};"
+    "interface Foo : FooParent { constructor(); };"
   );
 idlArray.add_objects({
   Foo: ["new Foo()"],
   FooParent: ["new FooParent()"]
 });
 idlArray.test();
 </script>
 <script type="text/json" id="expected">

--- a/testing/web-platform/tests/resources/test/tests/unit/IdlInterface/constructors.html
+++ b/testing/web-platform/tests/resources/test/tests/unit/IdlInterface/constructors.html
@@ -3,23 +3,24 @@
 <div id="log"></div>
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script src="/resources/WebIDLParser.js"></script>
 <script src="/resources/idlharness.js"></script>
 <script src="../../../idl-helper.js"></script>
 <script>
 "use strict";
+// [Constructor] extended attribute should not be supported:
 test(function() {
     var i = interfaceFrom('[Constructor] interface A { };');
-    assert_equals(i.constructors().length, 1);
+    assert_equals(i.constructors().length, 0);
 }, 'Interface with Constructor extended attribute.');
 
 test(function() {
     var i = interfaceFrom('interface A { constructor(); };');
     assert_equals(i.constructors().length, 1);
 }, 'Interface with constructor method');
 
 test(function() {
-    var i = interfaceFrom('[Constructor] interface A { constructor(); };');
+    var i = interfaceFrom('interface A { constructor(); constructor(any value); };');
     assert_equals(i.constructors().length, 2);
-}, 'Interface with both');
+}, 'Interface with constructor overloads');
 </script>

--- a/testing/web-platform/tests/web-animations/interfaces/Animation/constructor.html
+++ b/testing/web-platform/tests/web-animations/interfaces/Animation/constructor.html
@@ -68,17 +68,17 @@ for (const args of gTestArguments) {
   test(t => {
     const effect = args.createEffect();
     const animation = new Animation(effect, args.timeline);
 
     assert_not_equals(animation, null,
                       'An animation sohuld be created');
     assert_equals(animation.effect, effect,
                   'Animation returns the same effect passed to ' +
-                  'the Constructor');
+                  'the constructor');
     assert_equals(animation.timeline, args.expectedTimeline,
                   'Animation timeline should be ' + args.expectedTimelineDescription);
     assert_equals(animation.playState, 'idle',
                   'Animation.playState should be initially \'idle\'');
   }, 'Animation can be constructed ' + args.description);
 }
 
 test(t => {

--- a/testing/web-platform/tests/webvr/idlharness.https.html
+++ b/testing/web-platform/tests/webvr/idlharness.https.html
@@ -139,18 +139,19 @@ interface VRPose {
   readonly attribute Float32Array? linearVelocity;
   readonly attribute Float32Array? linearAcceleration;
 
   readonly attribute Float32Array? orientation;
   readonly attribute Float32Array? angularVelocity;
   readonly attribute Float32Array? angularAcceleration;
 };
 
-[Constructor]
 interface VRFrameData {
+  constructor();
+
   readonly attribute Float32Array leftProjectionMatrix;
   readonly attribute Float32Array leftViewMatrix;
 
   readonly attribute Float32Array rightProjectionMatrix;
   readonly attribute Float32Array rightViewMatrix;
 
   readonly attribute VRPose pose;
 };
@@ -177,18 +178,18 @@ partial interface Navigator {
 
 enum VRDisplayEventReason {
   "mounted",
   "navigation",
   "requested",
   "unmounted"
 };
 
-[Constructor(DOMString type, VRDisplayEventInit eventInitDict)]
 interface VRDisplayEvent : Event {
+  constructor(DOMString type, VRDisplayEventInit eventInitDict);
   readonly attribute VRDisplay display;
   readonly attribute VRDisplayEventReason? reason;
 };
 
 dictionary VRDisplayEventInit : EventInit {
   required VRDisplay display;
   VRDisplayEventReason reason;
 };