What happens when an invalid JSON string is deserialized using JavaScriptSerializer?

When an invalid JSON string is deserialized using JavaScriptSerializer, an ArgumentException is thrown. This behavior occurs because the JavaScriptSerializer is designed to validate the structure and syntax of the JSON string before conversion into an object or data structure. If the JSON string does not conform to valid JSON formatting—such as incorrect bracket usage, mismatched quotes, or other syntax errors—the serializer recognizes these issues as improper data and responds accordingly by raising an ArgumentException. This is a critical feature for developers, as it allows them to catch and handle errors effectively when working with JSON data, ensuring that the application can respond appropriately to incorrect input and maintain robustness.

In contrast, other possible outcomes like returning null, logging an error, or ignoring the error silently do not align with the strict error handling mechanism employed by JavaScriptSerializer. The serializer's approach guarantees that invalid JSON is acknowledged rather than being passed through silently or producing ambiguous outcomes. This promotes better error handling and debugging practices in application development.