Fixes #81762

src/vs/base/browser/mouseEvent.ts

@@ -152,8 +152,16 @@ export class StandardWheelEvent {
 		this.deltaX = deltaX;
 
 		if (e) {
-			if (e.type === 'wheel') {
+			// Old (deprecated) wheel events
+			let e1 = <IWebKitMouseWheelEvent><any>e;
+			let e2 = <IGeckoMouseWheelEvent><any>e;
 
+			// vertical delta scroll
+			if (typeof e1.wheelDeltaY !== 'undefined') {
+				this.deltaY = e1.wheelDeltaY / 120;
+			} else if (typeof e2.VERTICAL_AXIS !== 'undefined' && e2.axis === e2.VERTICAL_AXIS) {
+				this.deltaY = -e2.detail / 3;
+			} else if (e.type === 'wheel') {
 				// Modern wheel event
 				// https://developer.mozilla.org/en-US/docs/Web/API/WheelEvent
 				const ev = <WheelEvent><unknown>e;
@@ -161,22 +169,9 @@ export class StandardWheelEvent {
 				if (ev.deltaMode === ev.DOM_DELTA_LINE) {
 					// the deltas are expressed in lines
 					this.deltaY = -e.deltaY;
-					this.deltaX = -e.deltaX;
 				} else {
 					this.deltaY = -e.deltaY / 40;
-					this.deltaX = -e.deltaX / 40;
 				}
-
-			} else {
-				// Old (deprecated) wheel events
-				let e1 = <IWebKitMouseWheelEvent><any>e;
-				let e2 = <IGeckoMouseWheelEvent><any>e;
-
-				// vertical delta scroll
-				if (typeof e1.wheelDeltaY !== 'undefined') {
-					this.deltaY = e1.wheelDeltaY / 120;
-				} else if (typeof e2.VERTICAL_AXIS !== 'undefined' && e2.axis === e2.VERTICAL_AXIS) {
-					this.deltaY = -e2.detail / 3;
 			}
 
 			// horizontal delta scroll
@@ -188,6 +183,17 @@ export class StandardWheelEvent {
 				}
 			} else if (typeof e2.HORIZONTAL_AXIS !== 'undefined' && e2.axis === e2.HORIZONTAL_AXIS) {
 				this.deltaX = -e.detail / 3;
+			} else if (e.type === 'wheel') {
+				// Modern wheel event
+				// https://developer.mozilla.org/en-US/docs/Web/API/WheelEvent
+				const ev = <WheelEvent><unknown>e;
+
+				if (ev.deltaMode === ev.DOM_DELTA_LINE) {
+					// the deltas are expressed in lines
+					this.deltaX = -e.deltaX;
+				} else {
+					this.deltaX = -e.deltaX / 40;
+				}
 			}
 
 			// Assume a vertical scroll if nothing else worked
@@ -196,7 +202,6 @@ export class StandardWheelEvent {
 			}
 		}
 	}
-	}
 
 	public preventDefault(): void {
 		if (this.browserEvent) {