I'm trying to make an Undo function for canvas drawing, but the issue…

… is, i'm dumb

src/app/shared/model/whiteboard.service.ts

@@ -67,7 +67,7 @@ export class WhiteboardService {
 			path
 		};
 
-		const whiteboardMarkings = this.af.database.list('whiteboardMarkings/' + key);
+		const whiteboardMarkings = this.getMarkings(key);
 		return Observable.from([whiteboardMarkings.push(marking)]);
 	}
 

src/app/whiteboard/whiteboard.component.ts

@@ -68,6 +68,7 @@ export class WhiteboardComponent implements OnInit, OnChanges, OnDestroy {
 		if (this.markings) {
 			this.markingsToCanvas(this.markings);
 		}
+		document.addEventListener('keydown', this.keyboardInput);
 	}
 
 	ngOnChanges(changes: SimpleChanges) {
@@ -224,6 +225,17 @@ export class WhiteboardComponent implements OnInit, OnChanges, OnDestroy {
 		}
 	}
 
+	keyboardInput(event: KeyboardEvent) {
+		if (event.keyCode == 90 && event.ctrlKey) {
+			window.alert("Undo"); 
+			var newMarks = [];
+			for (var i = 0; i < (this.markings.length - 1); ++i) {
+				newMarks[i] = this.markings[i];
+			}
+			this.markingsToCanvas(newMarks);
+		}
+	}
+
 	cursorPoint(event) {
 		// Return a paper.js point where the mouse is at relative to the canvas
 		const canvasPos = this.canvasEl.getBoundingClientRect();