The issue I had with Pyjamas is that the whole tool-chain and compilation was a bit borked and the documentation a bit vague. After playing around with it for a day I decided it was too cumbersome so I ditched it in the end and tried py2js which Pyjaco is forked from. Mind you that was 2 years ago so a lot might have improved in that time but it convinced me that writing JS in Python is (was) not really feasible.