AWS Lambda Node error logging: Is it necessary to separately log the stack?

Question

Some of the example code in the AWS Javascript SDK docs log the stack of an error separately to the error itself, for example this is from the AWS.CloudWatch overview:

var cloudwatch = new AWS.CloudWatch();
cloudwatch.getMetricWidgetImage(params, function (err, data) {
  if (err) console.log(err, err.stack); // an error occurred
  else     console.log(data);           // successful response
});

So far as I can tell, this is redundant in Node (I have only tested on v10.16). If I log just the error object, it includes the stack trace:

> console.log(e)
Error: x
    at repl:2:8
    at Script.runInThisContext (vm.js:122:20)
    at REPLServer.defaultEval (repl.js:332:29)
    at bound (domain.js:402:14)
    at REPLServer.runBound [as eval] (domain.js:415:12)
    at REPLServer.onLine (repl.js:642:10)
    at REPLServer.emit (events.js:198:13)
    at REPLServer.EventEmitter.emit (domain.js:448:20)
    at REPLServer.Interface._onLine (readline.js:308:10)
    at REPLServer.Interface._normalWrite (readline.js:451:12)
undefined

Whereas if I log both, as Amazon have done above, I get an ugly ouput with duplication:

> console.log(e, e.stack)
Error: x
    at repl:2:8
    at Script.runInThisContext (vm.js:122:20)
    at REPLServer.defaultEval (repl.js:332:29)
    at bound (domain.js:402:14)
    at REPLServer.runBound [as eval] (domain.js:415:12)
    at REPLServer.onLine (repl.js:642:10)
    at REPLServer.emit (events.js:198:13)
    at REPLServer.EventEmitter.emit (domain.js:448:20)
    at REPLServer.Interface._onLine (readline.js:308:10)
    at REPLServer.Interface._normalWrite (readline.js:451:12) 'Error: x\n    at repl:2:8\n    at Script.runInThisContext (vm.js:122:20)\n    at REPLServer.defaultEval (repl.js:332:29)\n    at bound (domain.js:402:14)\n    at REPLServer.runBound [as eval] (domain.js:415:12)\n    at REPLServer.onLine (repl.js:642:10)\n    at REPLServer.emit (events.js:198:13)\n    at REPLServer.EventEmitter.emit (domain.js:448:20)\n    at REPLServer.Interface._onLine (readline.js:308:10)\n    at REPLServer.Interface._normalWrite (readline.js:451:12)'
undefined

Is there some reason that Amazon are using the console.log(err, err.stack) pattern that I am missing if I just do console.log(err)?

(I am primarily using Node in an AWS Lambda, version 10.x)

Possibly a carryover from older Node.js behavior, mentioned at https://stackoverflow.com/a/33593443/1695906 — Michael - sqlbot, Nov 28 '19 at 00:19
Thanks @Michael - sqlbot, yes, that explains it: it was required for Node < 6. If you convert your comment to an answer, I will accept it. — Rich, Nov 28 '19 at 10:08

score 0 · Accepted Answer · answered Dec 03 '19 at 10:12

The console.log(err, err.stack) formula was required for Node versions < 6, as they did not log the error stack by default.

More recent Node versions can just do console.log(err).

See https://stackoverflow.com/a/33593443/1695906 for a bit more detail

(The oldest Node offered by AWS Lambda at the time of writing is Node.js 8.10, so perhaps AWS should update their docs now to remove this.)

(From "@Michael - sqlbot"'s comment, thanks!)

AWS Lambda Node error logging: Is it necessary to separately log the stack?

1 Answers1