Javascript error: 'base64' is undefined

We prefer to have the dependency to base64.js added to the module.

Also see https://www.drupal.org/node/1181070

The problem here is that rc4_email_preprocess_html() is not always excecuted (e.g. for the imce popup). This in turn results in a JavaScript error on IE browsers as it doesn't find the base64 dependency.

So I would either do a check on Drupal.settings.rc4_email if it is set before performing any actions:

if (Drupal.settings.rc4_email !== undefined) {}

Or implement hook_libraries_info to provide base64 as a library as some projects may not want to have a dependency to an external resource.

New patch with test if Drupal.settings.rc4_email is set.

Indeed