But if u could program the front and the back in a single language which would u prefer
Python is not supported for front-end (yet??). So the choice is quite easy.
If you want to stick a single language for both front and backend, using JS is the best solution.
I am just asking a hypothetical question, what if you could do everything in python and every thing in js. Would you still use js cause you like the language or use python.
JS is also for back-end. Maybe you have never heard about Nodejs or io.js