js-runtime/runtime-checker.js

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);
}

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));
			}
		}
	});
}