LibJS: Add Function() and Function.prototype

Author: https://github.com/linusg
Commit: 2944039d6b
Pull-request: https://github.com/SerenityOS/serenity/pull/1622
Reviewed-by: https://github.com/awesomekling ✅

Libraries/LibJS/AST.cpp

@@ -333,6 +333,8 @@ Value UnaryExpression::execute(Interpreter& interpreter) const
         case Value::Type::String:
             return js_string(interpreter, "string");
         case Value::Type::Object:
+            if (lhs_result.as_object().is_function())
+                return js_string(interpreter, "function");
             return js_string(interpreter, "object");
         case Value::Type::Boolean:
             return js_string(interpreter, "boolean");