How to add debug code to core package?

i try to add a oauth function of my meteor app. but it reports unrecognized login options, i tracked the error message it comes from package accounts-base, i try to add console.log command in the code to print the options to see what is it. but after i changed the js file, meteor crashed. i can’t start my meteor app . i have to reinstalled meteor to make my meteor app works again.
how to add console.log command in accounts-base/os/accounts-server.js?