Error in callback doesn't display error info

Question

Sails.js 1.0.2

Hi. I try to debug an error in a callback but the only message is this one:

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    WARNING: Something seems to be wrong with this function.
    It is trying to signal that it has finished AGAIN, after
    already resolving/rejecting once.
    (silently ignoring this...)

    To assist you in hunting this down, here is a stack trace:

    ```
    at /node/zg-sails-v1/node_modules/sails-mongo/lib/private/do-with-connection.js:242:28
    at /node/zg-sails-v1/node_modules/sails-mongo/lib/private/do-with-connection.js:123:18
    at Object.success (/node/zg-sails-v1/node_modules/sails-mongo/lib/private/build-std-adapter-method.js:61:47)
    at /node/zg-sails-v1/node_modules/machine/lib/private/help-build-machine.js:1509:30
    at proceedToFinalAfterExecLC (/node/zg-sails-v1/node_modules/parley/lib/private/Deferred.js:1151:14)
    at proceedToInterceptsAndChecks (/node/zg-sails-v1/node_modules/parley/lib/private/Deferred.js:909:12)
    at proceedToAfterExecSpinlocks (/node/zg-sails-v1/node_modules/parley/lib/private/Deferred.js:841:10)
    at /node/zg-sails-v1/node_modules/parley/lib/private/Deferred.js:303:7
    at /node/zg-sails-v1/node_modules/machine/lib/private/help-build-machine.js:964:24
    at Function.handlerCbs.success (/node/zg-sails-v1/node_modules/machine/lib/private/help-build-machine.js:824:26)
    at findCb (/node/zg-sails-v1/node_modules/sails-mongo/lib/private/machines/find-records.js:138:20)
    at handleCallback (/node/zg-sails-v1/node_modules/mongodb/lib/utils.js:120:56)
    at /node/zg-sails-v1/node_modules/mongodb/lib/cursor.js:860:16
    at handleCallback (/node/zg-sails-v1/node_modules/mongodb-core/lib/cursor.js:171:5)
    at setCursorDeadAndNotified (/node/zg-sails-v1/node_modules/mongodb-core/lib/cursor.js:505:3)
    at nextFunction (/node/zg-sails-v1/node_modules/mongodb-core/lib/cursor.js:651:7)
    at Cursor.next [as _next] (/node/zg-sails-v1/node_modules/mongodb-core/lib/cursor.js:692:3)
    at fetchDocs (/node/zg-sails-v1/node_modules/mongodb/lib/cursor.js:856:10)
    at /node/zg-sails-v1/node_modules/mongodb/lib/cursor.js:879:7
    at handleCallback (/node/zg-sails-v1/node_modules/mongodb-core/lib/cursor.js:171:5)
    at nextFunction (/node/zg-sails-v1/node_modules/mongodb-core/lib/cursor.js:682:5)
    at /node/zg-sails-v1/node_modules/mongodb-core/lib/cursor.js:593:7
    ```

I only want to display error infos. There's a stack trace following but it doesn't help me.

Here an example of my code:

User.find({id: id}).exec((err, user) => {
  if (err) {
    ...
  } else {
    ...
    console.log(myUndefinedVar);
  }
});

It's a legacy project with hundred of callbacks, so I can't refactor all the code with await, try / catch.

Thanks.

EDIT: Stacktrace added

---

EDIT: new example, eslint doesn't hang out.

Game.find({id: req.session.gameID}).exec((err, objGame) => {
    if (err) {
        utilService.newLog('error', stackTrace, __line, 'Game.find({id: req.session.gameID: ' + req.session.gameID + ' ...');
        utilService.newLog('error', stackTrace, __line, err);
        return res.redirect('dashboard');
    } else if (typeof objGame === 'undefined') {
        utilService.newLog('error', stackTrace, __line, 'objGame === undefined ...');
        utilService.newLog('error', stackTrace, __line, err);
        return res.redirect('dashboard');
    } else {
        ...
    }
});

This

Game.find({id: req.session.gameID}).exec((err, objGame) => {

objGame is an array

    } else if (typeof objGame === 'undefined') {

    ... 

    jsfiles = sails.config.gameCfg[objGame.type].dev.jsfiles;

Must be

    } else if (typeof objGame[0] === 'undefined') {

Because objGame[0] is undefined

No error is displayed, just the WARNING.

Answer 1

Had these errors so many times. Helped just one thing - switching all callbacks into async functions. Then i can see the errors.

Wrong:

function some_method() {
  User.find().limit(1).exec(function(err, users) {
    if(err) console.log(err);
    console.log(users[1].id)
    // i will get the error "WARNING: Something..."
    // because i am querying just 1 User, and trying to log second user 
  });
}

Good:

async function some_method() {
  var users = await User.find().limit(1);
  console.log(users[1].id)
  // i will see the exact error , which shows exactly where is the problem
  // and say, that i am trying to read property id of undefined.
  // You dont even need to console the Errors - it does it automatically!
}

But if your whole project is full with callbacks, what at least helps is to spot when the problems appears. As this message is not helping to know where at all is the problem. It can be anywhere in the whole project. What you can do - is Temporary deal with those prolems until you replace all your code from callback to async.

1) create Logging system. Log every request. I am using winston. Logging every request, writing request time with milliseconds. If you use pm2, dont write these request logs into console, because then you cant see when the real error occurs.

Next:

2) overwrite this WARNING to write the time when did it appear. Go to node_modules/parley/lib/private/Deffered.js , there are 2 places where this WARNING is written. replace it to: (new Date()) + '---' + (new Date().getTime()) + '---WARNING: Something seems to be wrong with this function...

So now you can at least know which request is buggy. If the project is almost abandoned, this way helps. But if the project is active, you should just rewrite every method into async await. I am already 6 months into this - rewriting the whole backend into async-await and it helps really well - code is much nicer, all errors very clear.

Answer 2

If you use create, update or find, then use await .

var new game = await Game.find({id: req.session.gameID}).exec((err, objGame) => {
    if (err) {
        utilService.newLog('error', stackTrace, __line, 'Game.find({id: req.session.gameID: ' + req.session.gameID + ' ...');
        utilService.newLog('error', stackTrace, __line, err);
        return res.redirect('dashboard');
    } else if (typeof objGame === 'undefined') {
        utilService.newLog('error', stackTrace, __line, 'objGame === undefined ...');
        utilService.newLog('error', stackTrace, __line, err);
        return res.redirect('dashboard');
    } else {
        ...
    }
});

But be sure, your function is an async function fn: async function () {}