Node.js exception handling
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The document discusses best practices for exception handling in Node.js, emphasizing the distinction between operational and programmer errors. It recommends using try/catch for asynchronous code and handling errors through callbacks or logging. Additionally, the document highlights the importance of automated testing and proper error class structures.
Node.js exception handling
- 1. Node.js Exception Handling Do it the right way Minh Hoang - http://minhhoang.de
- 2. Node.js • is a 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 for dealing 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 … think about this
- 12. Function - write it the right way - • first argument ist error • last ist callback • use return (return callback(null, data); or return(err)
- 13. Sources • Error Handling 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 will find a way, or I will make one” –Philip Sidney