Function.prototype.toString Change Proposal

Garrett Smith dhtmlkitchen at
Fri Sep 18 01:11:52 PDT 2009

On Fri, Sep 18, 2009 at 12:26 AM, Oliver Hunt <oliver at> wrote:
> How?
> javascript: alert(function(){})
> Safari 4 elerts:
> "function () {}"
> The current specification doesn't allow that.
> Why not?
> The current specification requires the result of
> Function.prototype.toString to be a FunctionDeclaration and
> "function(){}" is not  a FunctionDeclaration representation.
> So it seems you want Safari to change, but the specification to
> remain. I would have to disagree, as that might break sites (and for
> absolutely no good reason).
> I propose that browsers today stay as they are (Safari, Firefox,
> Chrome, IE, etc all produce that result).  The specification should
> allow them to do so.
> I was referring mainly to the changes in representation of the native
> functions sorry.

That would be an implementation's choice. Opera does that for some
non-ecma functions (like alert), but not for parseInt.

javascript: alert([parseInt, alert, function(){}].join('\n'));
function () { [native code] }
function alert() { /* source code not available */ }

1) not legal
2) legal
3) not legal

 I'm also unsure whether it would be possible to add
> 'anonymous' as a function name.

I don't think an Identifier should be required and browsers do return
a FunctionExpression with no Identifier for that case (
(function(){}).toString() ). I see no reason to require a change in
that. Instead, the spec should allow that behavior.

The proposed change in the text is to replace "Function Declaration"
with "Function Definition". That means that FunctionExpression
representation where the Identifier is optional (and usually omitted)
would be legal.

I really can't see how that would cause any compatibility issues. If
anything, it should help absolve the currently non-conforming (major)

I vaguely recall one site failing when we
> removed the space on either side of the ()'s so that does worry me.

That is the "implementation dependent" part.

Here is the complete proposed text, again:-

| Function.prototype.toString ( )
| An implementation-dependent representation of the
| function is returned. This representation has the
| syntax of a Function Definition. Note in particular
| that the use and placement of white space, line
| terminators, and semicolons within the representation
| string is implementation-dependent.

I also
> believe the eBay (at least in the past) did string replacement on the result
> of function.toString to create new functions which caused us a headache back
> then as well.

I bet it did!


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