CODEWITHSUNDEEP
node.jsexpresslogging
Rodrigo Sasaki
Rodrigo Sasaki

Reputation: 7226

How do I know which exception occurred when my app crashed?

I am working on a NodeJS module, and I have the following problem:

When some error occurs in the promise chain, I can handle the exception, log it to my centralized logging tool, and all is well.

However, from time to time I see some errors that right out crash the application, and it restarts leaving me with nothing to go on. Only when I look into the logs in the machine that I can figure out what is going on. The latest one was this:

TypeError: Converting circular structure to JSON

How can I log the error that crashes the application to a centralized log tool. I understand that if the app died it can't do anything. But there must be a strategy to do this

Upvotes: 0

Views: 118

Answers (3)

Terry Lennox
Terry Lennox

Reputation: 30715

You can try a logging library such as Winston with the express-winston module express-winston this provides error logging middleware, for example: 

  var express = require('express');
  var expressWinston = require('express-winston');
  var winston = require('winston');
  var app = express();

  app.use(expressWinston.logger({
      transports: [
        new winston.transports.File({ filename: 'express.log' })
      ],
      format: winston.format.combine(
        winston.format.json()
      )
  }));

  app.get('/test', function(req, res, next) {
      res.send('All good');
  });

  app.get('/error', function(req, res, next) {
      // Let's cause an error.
      let r = JSON.stringify(req);
  });

  app.listen(3000, function(){
      console.log(`Express Listening on port ${this.address().port}`);
  });

  app.use(expressWinston.errorLogger({
      transports: [
          new winston.transports.File({ filename: 'express-error.log' })
      ],
      format: winston.format.combine(
          winston.format.json()
      )
  }));

Upvotes: 0

narayansharma91
narayansharma91

Reputation: 2353

Best way to handle the exception is to create one helper function where you must configure with error logging tool like (rollbar in heroku), and in every function/routes, you must include your source code inside the try-catch block. Write your code inside the try section and use the helper function and pass the exception to the helper file. It will look like this

//helper.js

const handleException = (exception) => {
//configure your error logging tool here.
}
const internalServerError = env => (err, req, res, next) => {
  if (!err) {
    return next();
  }
  handleException(err)//utilize common handler
};

module.exports = { handleException }

and in the main file

//app.js
const { handleException, internalServerError } = required('helper');
app.post((req, res) => {
   try {
      //your code will goes here
   } catch(err) {
     handleException(err)//you can customize error as per requirements
   }
});

//uncatch exception will trigger here. Put this bottom of the routes file. 
 app.use(internalServerError());

Upvotes: 1

Charlie
Charlie

Reputation: 23848

Place inside try/catch block any expression that might generate an error . Handle the error there or forward it with new information attached.

try {

   suspectedFunction()
}
catch(e) {

   logError(e)

   if (necessary){
     e.parseSuccess = false;
     throw e
   }

}

Upvotes: 0

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