894446 - Suggestion: improve the default string serialization (toString) of Error objects

Status: RESOLVED INVALID

(Core :: JavaScript Engine, enhancement)

Description

[Kyle Simpson]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:24.0) Gecko/20130713 Firefox/24.0 (Nightly/Aurora)
Build ID: 20130713004004

Steps to reproduce:

Run this code, like in the console.

```
function blah() {
   function foo() {
      var a = true;
      try { a(); }
      catch (err) { console.log(err+""); }
   }
   foo();
}

blah();
```


Actual results:

Outputs: "TypeError: boolean is not a function" but omits the stack trace info that was available on the error object. The stack trace is often very helpful.


Expected results:

It would be very nice if the default toString() of Error objects also included Firefox's `.stack` property from the Error instance.

I've created a simple hopefill/polyfill snippet for what that could/would look like:

https://gist.github.com/getify/6009932

-------------

Both Chrome and Firefox track this very helpful `.stack` property, so it'd be nice if both browsers outputted it by default. My hopefill/polyfill normalizes the behavior between Chrome and Firefox.

Comment 1

[Kyle Simpson]

BTW, I filed the exact same suggestion over at Chrome's bug tracker: https://code.google.com/p/chromium/issues/detail?id=260740

Comment 2

[Kyle Simpson]

Also, of note, the JS specification leaves the implementation of Error.prototype.toString up to browser vendors, so that's not a blocker to making changes as I propose. Of course, I filed this with both FF and Chrome because I'd like to see all browsers provide this better output by default rather than having to work harder to get it. :)

Comment 3

[Jeff Walden [:Waldo]]

I'm not sure what JS spec you're looking at.  ES5 specifies a precise algorithm for Error.prototype.toString, which if memory serves we follow exactly.

http://es5.github.io/#x15.11.4.4

Comment 4

[Kyle Simpson]

Ah, I see. I was asserting that based on MDN's page for `Error.prototype.toString`:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/toString

"According to ECMA-262, implementations are free to decide the behavior of this method."

I guess this page hasn't been updated since ES5 specified the behavior.

I'll take my suggestion to ES instead.