Add typed variables

example.html

@@ -1,4 +1,5 @@
 <script src="runtime-checker.js"></script>
+
 <script>
 	const sum = typedFunction((a_number, b_number) => {
 		return a + b;
@@ -8,5 +9,14 @@
 	console.log(result); // 3
 
 	sum("1", 2); // Error
+
+</script>
+
+<script>
+	typedVar("test", 5);
+
+	test = 6;
+
+	test = "a string"; // Error
 </script>
 

runtime-checker.js

@@ -59,3 +59,22 @@ window.typedFunction = function(func) {
 	return func.addRuntimeChecker();
 }
 
+window.typedVar = function(name, value) {
+	function getTypeName(type) {
+		return typeof type === "function" ? type.name : typeof type;
+	}
+
+	var scope = typedVar.caller || window;
+
+	Object.defineProperty(scope, name, {
+		set: function(newValue) {
+			if (
+				(typeof value === "function" && !(newValue instanceof value)) ||
+				(typeof value !== "function" && typeof newValue !== typeof value)
+			) {
+				throw new Error("Cannot assign value of type " + getTypeName(newValue) + " to variable " + name + " of type " + getTypeName(value));
+			}
+		}
+	});
+}
+