However, there is a better way especially for some frequently used functions. You can put them in a .js file and re-use them across your reports. Here is how to do it.
1. Create a set of Java Script functions (such as for logging, modifying your queries, etc) and put it in a file. (e.g. GbsFunctions.js)
2. Save the file under somewhere under your resource directory, which can be set using Window->Preferences->Report Design->Resource->Resource folder within Eclipse. (e.g. resourcedir/GBS/scripts/GbsFunctions.js).
3. Now add the following XML tag to your XML source of the reports. Make sure that the XML you add doesn't result in malformed XML. (e.g. add just before <data-sources>
4. Now, you can access the functions listed in GbsFunctions.js within BIRT.
Hope you find this useful.