I particularly like this because it doesn't interfere with the flow of the commit message's first line in explaining what it does. There are too many commits out there that waste half the first line with the ticket number, area of code, etc.

Instead of 'JAT-1241: app/index.js(opt): Optimised the index', 'Optimised the index' should be fine. Tools can understand that, and can already work out which files changed.