From 0455d91928e270cd3f2e2798208ca1dfd1123aa1 Mon Sep 17 00:00:00 2001
From: filifa <filifa.breath652@8alias.com>
Date: Thu, 11 Dec 2025 23:49:34 -0500
Subject: [PATCH] add backspace function

---
 main.js | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/main.js b/main.js
index 7a80389..a3ed6e6 100644
--- a/main.js
+++ b/main.js
@@ -178,6 +178,32 @@ function keyPress(c) {
 	currentInput.setSelectionRange(selectionStart+1, selectionStart+1);
 }
 
+function backspace() {
+	currentInput.focus();
+	if (selectionEnd === 0) {
+		return;
+	}
+
+	let begin = null;
+	if (selectionStart === selectionEnd) {
+		begin = currentInput.value.slice(0, selectionStart-1);
+	} else {
+		begin = currentInput.value.slice(0, selectionStart);
+	}
+
+	const end = currentInput.value.slice(selectionEnd);
+
+	currentInput.value = begin + end;
+
+	if (selectionStart === 0) {
+		currentInput.setSelectionRange(0, 0);
+	} else if (selectionStart === selectionEnd) {
+		currentInput.setSelectionRange(selectionStart-1, selectionStart-1);
+	} else {
+		currentInput.setSelectionRange(selectionStart, selectionStart);
+	}
+}
+
 document.querySelector("#expr").addEventListener("focus", setCurrentInput);
 document.querySelector("#modulus").addEventListener("focus", setCurrentInput);
 
@@ -205,5 +231,6 @@ document.querySelector("#pow").addEventListener("click", () => keyPress("^"));
 document.querySelector("#clear").addEventListener("click", clear);
 document.querySelector("#enter").addEventListener("click", calculate);
 
-// TODO backspace might be tricky
+document.querySelector("#backspace").addEventListener("click", backspace);
+
 // TODO implement square root and inverse keys