From 18294b0606db259e7036d0c1a2f7531f0a37c227 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Thu, 7 Jan 2021 23:32:27 +0200
Subject: [PATCH] Stop a piece from capturing itself

---
 shatrizualizer.html | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/shatrizualizer.html b/shatrizualizer.html
index 09c461c..a15f829 100644
--- a/shatrizualizer.html
+++ b/shatrizualizer.html
@@ -306,6 +306,12 @@
 					renderedPromotion = whiteMove ? whitePieces[promotion] : blackPieces[promotion];
 				}
 
+				// Are we moving the piece onto itself?
+				if (startLetter === endLetter && startNumber === endNumber) {
+					alert('Start and end squares of the move cannot be identical');
+					return;
+				}
+
 				// Are we moving the piece from where it is located?
 				let startSquare = document.getElementById(startLetter + startNumber);
 				if (startSquare.childNodes.length === 0) {