Exception in AWS lambda function is empty

Question

I'm trying to serialize an exception in an AWS lambda function, but when I do it, the object has no properties. Here is a simplified version of this:

exports.handler = function(event, context) {
  try {
    var x = some.property;
    context.succeed(null);
  } catch (err) {
    console.log("error=" + JSON.stringify(err, null, 2));
    context.fail(err);
  }
};

Here's the log output. Note that when I JSON.stringify the exception object, there's nothing there, but in the context.fail line, the exception data is there.

START RequestId: 810913d1-567b-11e5-a0d1-95dad6b9184b
2015-09-08T22:46:55.308Z    810913d1-567b-11e5-a0d1-95dad6b9184b    error={}
2015-09-08T22:46:55.368Z    810913d1-567b-11e5-a0d1-95dad6b9184b    {"errorMessage":"some is not defined","errorType":"ReferenceError","stackTrace":["exports.handler (/var/task/index.js:5:17)"]}
END RequestId: 810913d1-567b-11e5-a0d1-95dad6b9184b
REPORT RequestId: 810913d1-567b-11e5-a0d1-95dad6b9184b  Duration: 174.72 ms Billed Duration: 200 ms     Memory Size: 128 MB Max Memory Used: 9 MB

Anyone know what might be happening?

Create custom output handler and that will solve your problem. — adamkonrad
– adamkonrad, Commented Sep 9, 2015 at 23:20

StickyCube · Accepted Answer · 2015-09-08 23:04:46Z

1

The properties of the Exception might have been defined with Object.defineProperty. if you run the following example, you'll see that they don't get serialized

function Exception () {
    this.message = function () {
        return 'Oh NOES';
    };
}

Exception.prototype.constructor = Exception;

Object.defineProperty(Exception.prototype, 'foo', {
    get: function () {
        return this.message();
    }
});

var e = new Exception();

console.log(e.foo) // 'Oh NOES'
console.log(JSON.stringify(e, null, 2)); // {}

answered Sep 8, 2015 at 23:04

StickyCube

1,7212 gold badges17 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

holly_cheng Over a year ago

Good thought, but console.log(err.errorMessage) returns undefined. :(

StickyCube Over a year ago

Interesting, what do the following things output with console.log: err.constructor, Object.getOwnPropertyNames(err), Object.keys(err) ?

holly_cheng Over a year ago

err.constructor=function ReferenceError() { [native code] }, getOwnPropertyNames=stack,arguments,type,message. So then I tried each of those 4 properties and they have their own values. So it looks like context.fail must take the native properties and then construct its own JSON for output. I don't know why I can't see those when I stringify the object, but at least I can figure out to get the data I need. Thanks!

Kostiantyn · Accepted Answer · 2024-12-27 05:13:13Z

0

Just found a very simple stupid option(s).

1 Prepend output with a string

console.error("message": "_" + error);

2 Use toString

console.error("message": error.toString());

3 Use message property

console.error("message": error.message);

All three work for me but might not work for you depending on your use case.

Hope that helps

answered Dec 27, 2024 at 5:13

Kostiantyn

1,8792 gold badges18 silver badges23 bronze badges

Collectives™ on Stack Overflow

Exception in AWS lambda function is empty

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related