No behavior is specified for when a "readAs" method on FileReader is called with invalid input. In Chromium 26.0.1410.40, no exception is thrown and the onerror callback is not invoked.
Chromium discussion thread:
Chromium behavior discussed on StackOverflow:
This is defined to throw TypeError. http://dev.w3.org/2006/webapi/WebIDL/#es-interface