Question

For every logger statement with any level, I need to display the file name from where the log statement executed, below is the illustration I given below:

Example :
Below is the line executed from JobWork.js

logger.info("getInCompleteJobs in job works");

Actual :

2012-11-05T06:07:19.158Z - info: getInCompleteJobs in job works

Required :

2012-11-05T06:07:19.158Z - info JobWork.js : getInCompleteJobs in job works

Without passing the fileName as a parameter from the log statement it should give the filename.

Answer 1

You can use the stack trace information attached to v8’s Error object to find out what file/line your code was called from. This approach works well, but it does not perform well; so you will want to disable it in production.

So you could do something like this:

  var logger_info_old = logger.info;
  logger.info = function(msg) {
    var fileAndLine = traceCaller(1);
    return logger_info_old.call(this, fileAndLine + ":" + msg);
  }

  /**
  * examines the call stack and returns a string indicating 
  * the file and line number of the n'th previous ancestor call.
  * this works in chrome, and should work in nodejs as well.  
  *
  * @param n : int (default: n=1) - the number of calls to trace up the
  *   stack from the current call.  `n=0` gives you your current file/line.
  *  `n=1` gives the file/line that called you.
  */
  function traceCaller(n) {
    if( isNaN(n) || n<0) n=1;
    n+=1;
    var s = (new Error()).stack
      , a=s.indexOf('\n',5);
    while(n--) {
      a=s.indexOf('\n',a+1);
      if( a<0 ) { a=s.lastIndexOf('\n',s.length); break;}
    }
    b=s.indexOf('\n',a+1); if( b<0 ) b=s.length;
    a=Math.max(s.lastIndexOf(' ',b), s.lastIndexOf('/',b));
    b=s.lastIndexOf(':',b);
    s=s.substring(a+1,b);
    return s;
  }