How do you enumerate over Error Objects in Javascript?

Question

I've looked around and have failed to find an answer to this.

What I am trying to do is print all the properties available in an Error object for error reporting. It may be impossible, but I would at least like to know why.

I have tried the following in Chrome and Firefox on Ubuntu 12.04.

try {
   throw new Error('Foo');
} catch (x) {
   console.log(Object.keys(x)); // []
   for (var i in x) console.log(i); // Prints nothing
}

Why not simply use console.dir(x); to see what's inside (mostly the stack function) ? — Denys Séguret
– Denys Séguret, Commented May 12, 2014 at 14:04
No. I need something to send back to the server for error reporting. — jdw
– jdw, Commented May 12, 2014 at 14:06

Bergi · Accepted Answer · 2014-05-12 14:11:06Z

5

The enumerability of Error object keys varies amongst browsers. Your best bet is to use Object.getOwnPropertyNames:

var props = Object.getOwnPropertyNames(x);
console.log(props);
for (var i=0; i<props.length; i++) console.log(x[props[i]]);

I need something to send back to the server for error reporting.

I'd go with explicitly naming the properties I'm interested in, for example:

reportErrorBack( JSON.stringify({
    name: e.name, // on the Error.prototype
    message: e.message,
    stack: e.stacktrace
});

edited May 12, 2014 at 14:11

answered May 12, 2014 at 14:05

Bergi

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1 Comment

jdw Over a year ago

Thanks for this. Do you know why you can't Enumerate over Error objects?

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