Add CSSOM View extensions to MouseEvent

Namely, x, y, pageX, pageY, offsetX, offsetY. Also updates screenX and screenY to not always coerce to integers.

Co-authored-by: Vinícius Francisco Xavier <viniciusfranciscoxavier@gmail.com>

lib/jsdom/living/events/MouseEvent-impl.js

@@ -5,8 +5,42 @@ const EventModifierMixinImpl = require("./EventModifierMixin-impl").implementati
 const UIEventImpl = require("./UIEvent-impl").implementation;
 
 const MouseEventInit = require("../generated/MouseEventInit");
+const { wrapperForImpl } = require("../generated/utils");
 
 class MouseEventImpl extends UIEventImpl {
+  get x() {
+    return this.clientX;
+  }
+  get y() {
+    return this.clientY;
+  }
+  get pageX() {
+    if (this._dispatchFlag) {
+      return 0;
+    }
+    const offset = wrapperForImpl(this.view)?.scrollX || 0;
+    return offset + this.clientX;
+  }
+  get pageY() {
+    if (this._dispatchFlag) {
+      return 0;
+    }
+    const offset = wrapperForImpl(this.view)?.scrollY || 0;
+    return offset + this.clientY;
+  }
+  get offsetX() {
+    if (this._dispatchFlag) {
+      return 0;
+    }
+    return this.pageX;
+  }
+  get offsetY() {
+    if (this._dispatchFlag) {
+      return 0;
+    }
+    return this.pageY;
+  }
+
   initMouseEvent(
     type,
     bubbles,

lib/jsdom/living/events/MouseEvent.webidl

@@ -7,7 +7,6 @@ interface MouseEvent : UIEvent {
   readonly attribute long screenY;
   readonly attribute long clientX;
   readonly attribute long clientY;
-
   readonly attribute boolean ctrlKey;
   readonly attribute boolean shiftKey;
   readonly attribute boolean altKey;
@@ -52,3 +51,27 @@ partial interface MouseEvent {
                         optional short buttonArg = 0,
                         optional EventTarget? relatedTargetArg = null);
 };
+
+// https://drafts.csswg.org/cssom-view/#extensions-to-the-mouseevent-interface
+// Adds attributes and changes existing ones to doubles
+partial interface MouseEvent {
+  readonly attribute double screenX;
+  readonly attribute double screenY;
+  readonly attribute double pageX;
+  readonly attribute double pageY;
+  readonly attribute double clientX;
+  readonly attribute double clientY;
+  readonly attribute double x;
+  readonly attribute double y;
+  readonly attribute double offsetX;
+  readonly attribute double offsetY;
+};
+
+// https://drafts.csswg.org/cssom-view/#extensions-to-the-mouseevent-interface
+// Changes existing coordinate entries to doubles
+partial dictionary MouseEventInit {
+  double screenX = 0.0;
+  double screenY = 0.0;
+  double clientX = 0.0;
+  double clientY = 0.0;
+};

test/web-platform-tests/to-upstream/html/editing/activation/click-event-properties.html

@@ -74,6 +74,12 @@
     assert_equals(e.screenY, 0);
     assert_equals(e.clientX, 0);
     assert_equals(e.clientY, 0);
+    assert_equals(e.x, 0);
+    assert_equals(e.y, 0);
+    assert_equals(e.pageX, 0);
+    assert_equals(e.pageY, 0);
+    assert_equals(e.offsetX, 0);
+    assert_equals(e.offsetY, 0);
 
     assert_equals(e.button, 0);
     assert_equals(e.buttons, 0);
@@ -84,4 +90,37 @@
 
 }, "clicking using click() should produce an event object with the correct MouseEventInit values");
 
+test(() => {
+  window.scrollX = 10;
+  window.scrollY = 20;
+  const e = new MouseEvent("click", {
+    clientX: 1, clientY: 2, view: window
+  });
+  assert_equals(e.x, 1);
+  assert_equals(e.y, 2);
+  assert_equals(e.pageX, 11);
+  assert_equals(e.pageY, 22);
+  assert_equals(e.offsetX, 11);
+  assert_equals(e.offsetY, 22);
+}, "MouseEvent should provide the correct computed values when the dispatch flag is not set");
+
+test(() => {
+  const e = new MouseEvent("click", {
+    screenX: 1.5, screenY: 2.5, clientX: 3.5, clientY: 4.5
+  });
+  assert_equals(e.screenX, 1.5);
+  assert_equals(e.screenY, 2.5);
+  assert_equals(e.clientX, 3.5);
+  assert_equals(e.clientY, 4.5);
+}, "MouseEvent.constructor should preserve doubles");
+
+test(() => {
+  const e = new MouseEvent("click");
+  e.initMouseEvent("click", true, true, null, null, 1.5, 2.5, 3.5, 4.5);
+  assert_equals(e.screenX, 1);
+  assert_equals(e.screenY, 2);
+  assert_equals(e.clientX, 3);
+  assert_equals(e.clientY, 4);
+
+}, "MouseEvent.initMouseEvent should convert doubles to longs");
 </script>