Node.js exception handling

Node.js exception handling

• 1.
  Node.js Exception Handling Do it the right way Minh Hoang - http://minhhoang.de
• 2.
  Node.js • isa still a relatively new programming language • Node.js crashes for any ‘uncatch error’ • Most developers are confused when to use • try/catch • pass error to a callback • throw an error
• 3.
  error vs. exception • an error = an instance of the Error class • can be created • can be thrown • can passed to callback • a thrown error = an Exception
• 4.
  errors Operational Errors (run-time issue, not bug) Programmer Errors (bug) • out-of-memory • connection issues • timeout • server return 500 HTTP code • socket hang-up • no ‘undefined’ check • no callback for asynchronous function • object type error a correct code must be able to deal with operation error
• 5.
  Best Practices fordealing with operation errors • Always put asynchronous code into try/catch (otherwise Node.js crashes if uncaught error happens) • Synchronous code: return error. • ENONT error why trying to open a file: create file the first before read it • socket hang-up: write code to reconnect if needed • ready to deal with invalid JSON - using try/catch • retry with 5xx HTTP error • no idea how to deal with unthinkable/-solvable issue - such as ENOMEM: log the error and crash (intentionally)
• 6.
  Dealing with programmer errors • crash immediately • how: throw new Error(‘ehh’); …. if you have a restarter in place (like Bluemix) …. or just use: forever.js
• 7.
  • instead of‘callback(result)’ use ‘callback(err, result)’ • because: either ‘result’ or ‘err’ is NULL!
• 8.
  Error class •has {name, message, stack} • if you create an Error instance manually, at least provide {name, message}
• 9.
  last chance… •use process.on(‘uncaughtException’, function() {<do_sth>}); —> Global Catch • it’s NOT recommended…but what if your app’s just crashed without leaving a trace?
• 10.
  Automated Test •Crucially important • start with unit-test for all modules • then integration test • no test, no CI, you are in the coding hell!
• 11.
  and … thinkabout this
• 12.
  Function - writeit the right way - • first argument ist error • last ist callback • use return (return callback(null, data); or return(err)
• 13.
  Sources • ErrorHandling in Node.js https:// www.joyent.com/developers/node/design/errors • Node.js Best Practices: http:// www.slideshare.net/the_undefined/nodejs-best-practices- 10428790 • Continuous Development: http:// blog.risingstack.com/continuous-deployment-of-node- js-applications/
• 14.
  “Either I willfind a way, or I will make one” –Philip Sidney