Instead of manually adding the .js scripts to your Cognos 8 Report Studio HTML item properties you are able to reference external .js files in your Cognos 8 Report Studio report.
You would have to add a HTML item with following syntax to your Cognos 8 report:
Where http://localhost:90/Cognos8 example of the gateway URI and MyJavaScriptFile.js is an external javascript file.
Steps:
1. Create a javascript file which you want to execute in Cognos 8 BI
2. Copy it to the webcontent directory
3. Create a sample report and add a HTML item to it
4. Add javascript to the HTML item like this one: