MouseEvent: fix {page,offset}{X,Y} during dispatch

Ensure that pageX and pageY reflect the coordinate relative to the origin of the document, i.e. clientX/clientY in the absence of scrolling support, during dispatch.

Also fix the target-relative coordinates, offsetX and offsetY, during dispatch. These will typically be (0, 0), e.g. in a synthetic click or a dispatched MouseEvent with default coordinates, but it will mirror clientX/clientY if those are set.

Lastly, remove some scrollX/scrollY logic for values computed outside of dispatch. While it logically followed the spec, scrolling is not implemented and it is unsafe to base the calculation on those replaceable properties.

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

@@ -5,7 +5,6 @@ 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() {
@@ -15,29 +14,19 @@ class MouseEventImpl extends UIEventImpl {
     return this.clientY;
   }
   get pageX() {
-    if (this._dispatchFlag) {
-      return 0;
-    }
-    const offset = wrapperForImpl(this.view)?.scrollX || 0;
-    return offset + this.clientX;
+    // TODO: consider dispatch flag and return page-relative event coordinate once layout is supported
+    return this.clientX; // TODO: add horizontal scroll offset once jsdom implements scrolling support
   }
   get pageY() {
-    if (this._dispatchFlag) {
-      return 0;
-    }
-    const offset = wrapperForImpl(this.view)?.scrollY || 0;
-    return offset + this.clientY;
+    // TODO: consider dispatch flag and return page-relative event coordinate once layout is supported
+    return this.clientY; // TODO: add vertical scroll offset once jsdom implements scrolling support
   }
   get offsetX() {
-    if (this._dispatchFlag) {
-      return 0;
-    }
+    // TODO: consider dispatch flag and return target-relative event coordinate once layout is supported
     return this.pageX;
   }
   get offsetY() {
-    if (this._dispatchFlag) {
-      return 0;
-    }
+    // TODO: consider dispatch flag and return target-relative event coordinate once layout is supported
     return this.pageY;
   }
 

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

@@ -91,19 +91,30 @@
 }, "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);
+  assert_equals(e.pageX, 1);
+  assert_equals(e.pageY, 2);
+  assert_equals(e.offsetX, 1);
+  assert_equals(e.offsetY, 2);
 }, "MouseEvent should provide the correct computed values when the dispatch flag is not set");
 
+async_test(t => {
+  const element = document.documentElement; // dispatch against something at the origin (0,0) so it passes in browsers
+  element.addEventListener("click", t.step_func_done(e => {
+    assert_equals(e.pageX, 1);
+    assert_equals(e.pageY, 2);
+    assert_equals(e.offsetX, 1);
+    assert_equals(e.offsetY, 2);
+  }));
+  element.dispatchEvent(new MouseEvent("click", {
+    clientX: 1, clientY: 2, view: window
+  }));
+}, "MouseEvent should provide the correct computed values when the dispatch flag is set");
+
 test(() => {
   const e = new MouseEvent("click", {
     screenX: 1.5, screenY: 2.5, clientX: 3.5, clientY: 4.5
@@ -121,6 +132,5 @@
   assert_equals(e.screenY, 2);
   assert_equals(e.clientX, 3);
   assert_equals(e.clientY, 4);
-
 }, "MouseEvent.initMouseEvent should convert doubles to longs");
 </script>