Make stack traces useful again

1-useless-stack.js

var fs = require('fs');

// Here is a simple function that reads a file and makes something with its content
function readLog1 (cb) {
  // Notice how I even gave a name to my callback, this is useful for stack traces, everyone says…
  fs.readFile('file-not-found.log', function onRead1 (err, content) {

    // Usual error handling
    if (err) return cb(err);

    // deal with content… not the point here
  });
}

// I run my function, and print the error
readLog1(function (err) { console.error('ERR 1', err.stack) });

// Here is the output:
/*

ERR 1 Error: ENOENT, open 'file-not-found.log'

*/
// Oh great, what am I supposed to do with that? No line number, nothing…
// What could I do in a real-life app to find *where* it failed?
// You faced even worse frustrating useless stack traces with DB modules

2-useful-stack.js

var fs = require('fs');

// Here is the same function
function readLog2 (cb) {
  // that does the same thing
  fs.readFile('file-not-found.log', function onRead2 (err, content) {

    // except it wraps received error in a new Error(…)
    if (err) return cb(new Error(err));

    // deal with content… not the point here
  });
}

// Run exactly the same way
readLog2(function (err) { console.error('ERR 2', err.stack) });

// But this time:
/*

ERR 2 Error: Error: ENOENT, open 'file-not-found.log'
    at onRead2 (/home/nchambrier/Projects/LMTM/ooz/2-userful-stack.js:9:24)
    at fs.js:207:20
    at Object.oncomplete (fs.js:107:15)

*/
// some useful output, I know WHERE it happened exactly
// and THAT's a stack worth storing in my logs

3-console-trace.js

var fs = require('fs');

// Here is the same function
function readLog3 (cb) {
  // that does the same thing
  fs.readFile('file-not-found.log', function onRead3 (err, content) {

    // not wrapping error cause I forgot it
    if (err) return cb(err);

    // deal with content… not the point here
  });
}

// This, let's use console.trace
readLog3(function (err) { console.trace('ERR 3', String(err)) });

// We get this:
/*

Trace: ERR 3 Error: ENOENT, open 'file-not-found.log'
    at /home/nchambrier/Projects/Perso/5480807/3-console-trace.js:16:35
    at onRead3 (/home/nchambrier/Projects/Perso/5480807/3-console-trace.js:9:21)
    at fs.js:207:20
    at Object.oncomplete (fs.js:107:15)

*/
// may be the best option, we don't rely on the called function to properly
// wrap error.
// Drawbacks:
// * It forces the way you should *log*, if you're writing a module which should
//   definitely not log itself, then you can't use that to be sure to provide
//   useful information to your user

// You can use Error.captureStackTrace for the same purpose:
readLog3(function (err) {
  var o = {};
  Error.captureStackTrace(o, handleError);
  console.error('ERR 3 (bis)', String(err), o.stack);
});

// I'm afraid you may lose the track in case of multiple async calls nested
// this has to be tested