commit cc2e2587f391b3c726f8c6bf809d1411fbc43cff
Author: ReimarPB <reimarpb@gmail.com>
Date:   Sat Sep 9 13:22:26 2023 +0200

    Initial commit

diff --git a/example.html b/example.html
new file mode 100644
index 0000000..b605496
--- /dev/null
+++ b/example.html
@@ -0,0 +1,15 @@
+<script src="runtime-checker.js"></script>
+<script>
+	function sum(a_number, b_number) {
+		return a + b;
+	}
+
+	// I need to get rid of this
+	sum = sum.addRuntimeChecker();
+
+	var result = sum(1, 2);
+	console.log(result); // 3
+
+	sum("1", 2); // Error
+</script>
+
diff --git a/runtime-checker.js b/runtime-checker.js
new file mode 100644
index 0000000..a32a49c
--- /dev/null
+++ b/runtime-checker.js
@@ -0,0 +1,58 @@
+Function.prototype.addRuntimeChecker = function() {
+	var handler = {
+		apply: function(target, thisArg, argumentValues) {
+			
+			// https://stackoverflow.com/a/31194949
+			var argumentNames = target.toString()
+				.replace(/[/][/].*$/mg,'') // strip single-line comments
+				.replace(/\s+/g, '') // strip white space
+				.replace(/[/][*][^/\*]*[*][/]/g, '') // strip multi-line comments  
+				.split('){', 1)[0].replace(/^[^(]*[(]/, '') // extract the parameters  
+				.replace(/=[^,]+/g, '') // strip any ES6 defaults  
+				.split(',').filter(Boolean); // split & filter [""]
+
+			var argumentNamesWithoutTypes = [];
+
+			for (var i = 0; i < argumentValues.length; i++) {
+				// Get type from parameter name
+				var match = argumentNames[i].match(/(.+)_(\w+)/);
+				if (!match || match.length < 3) {
+					argumentNamesWithoutTypes.push(argumentNames[i]);
+					continue;
+				}
+
+				argumentNamesWithoutTypes.push(match[1]);
+
+				var type = match[2];
+
+				// Check types
+				if (typeof argumentValues[i] !== type)
+					throw new Error("Invalid argument #" + i + " - Expected " + type + ", got " + typeof argumentValues[i]);
+			}
+
+			// Assign actual names to window object before calling functions
+			var oldWindow = {};
+			for (var i = 0; i < argumentNamesWithoutTypes.length; i++) {
+				var name = argumentNamesWithoutTypes[i];
+
+				oldWindow[name] = window[name];
+				window[name] = argumentValues[i];
+			}
+
+			// Call function
+			var runtimeCheckerResult = target.apply(thisArg, argumentValues);
+
+			// Re-assign old window values
+			for (var name in oldWindow) {
+				if (!oldWindow.hasOwnProperty(name)) continue;
+
+				window[name] = oldWindow[name];
+			}
+
+			return runtimeCheckerResult;
+		}
+	};
+
+	return new Proxy(this, handler);
+}
+