How to get console.log line numbers shown in Nodejs?

Question

Got an old application, that prints out quite a lot of messages using console.log, but I just can not find in which files and lines console.log is called.

Is there a way to hook into the app and show file name and line numbers?

Answer 1

Having full stack trace for each call is a bit noisy. I've just improved the @noppa's solution to print only the initiator:

['log', 'warn', 'error'].forEach((methodName) => {   const originalMethod = console[methodName];   console[methodName] = (...args) => {     let initiator = 'unknown place';     try {       throw new Error();     } catch (e) {       if (typeof e.stack === 'string') {         let isFirst = true;         for (const line of e.stack.split('\n')) {           const matches = line.match(/^\s+at\s+(.*)/);           if (matches) {             if (!isFirst) { // first line - current function                             // second line - caller (what we are looking for)               initiator = matches[1];               break;             }             isFirst = false;           }         }       }     }     originalMethod.apply(console, [...args, '\n', `  at ${initiator}`]);   }; }); 

It also patches other methods (useful for Nodejs, since warn and error don't come with a stack trace as in Chrome).

So your console would look something like:

Loading settings.json    at fs.readdirSync.filter.forEach (.../settings.js:21:13) Server is running on http://localhost:3000 or http://127.0.0.1:3000    at Server.app.listen (.../index.js:67:11)