set display to calculating using a timer

main.js

@@ -44,7 +44,9 @@ function evaluate() {
 	console.log(queue);
 
 	worker.postMessage({command: "compute", queue, m});
-	result.value = "calculating...";
+	timeoutId = setTimeout(() => {
+		document.querySelector("#result").value = "calculating...";
+	}, 500);
 }
 
 const expr = document.querySelector("#expr");
@@ -112,9 +114,11 @@ function switchButtons(enabled) {
 	}
 }
 
+let timeoutId = null;
 const worker = new Worker("./workers/compute.js");
 worker.addEventListener("message", (message) => {
 	document.querySelector("#result").value = message.data;
+	clearTimeout(timeoutId);
 });
 worker.addEventListener("error", (e) => {
 	console.log(e);