Update on ES3.1 block scoped function declarations

Allen Wirfs-Brock Allen.Wirfs-Brock at microsoft.com
Thu Jul 10 13:58:41 PDT 2008

Maybe, I'm missing something subtle, but 21 is clearly the right answer and is what I believe is specified by the version of section 10 that I sent out yesterday regardless of the scoping of block nested functions.  Of course, that's just spec-ware...

From: es4-discuss-bounces at mozilla.org [mailto:es4-discuss-bounces at mozilla.org] On Behalf Of Brendan Eich
Sent: Thursday, July 10, 2008 1:45 PM
To: Mark S. Miller
Cc: es3.x-discuss at mozilla.org; es4-discuss at mozilla.org; Herman Venter
Subject: Re: Update on ES3.1 block scoped function declarations

On Jul 10, 2008, at 1:28 PM, Mark S. Miller wrote:

On Thu, Jul 10, 2008 at 11:05 AM, Brendan Eich <brendan at mozilla.org<mailto:brendan at mozilla.org>> wrote:

So what would this program print in ES3.1?

const C = 42;
function f(x, y) {
  const C = 33;
  if (x) {
    const C = 21;
    return eval(y);
  return C;
print(f(true, "C"));


What does it print in ES4-opt-in?

Call it ES4, please. There's no point in playing games about opt-in, since we know we can't "break the web". ES3 added new syntax, so did ES2. No one bugged out about "opt-in".

21 is the right answer, although reflecting lexical blocks into something eval can see is a big pain (we did this in Firefox 2). It's a lot of work just for block-scoped const. Sorry if I missed the discussion, but was restricting const to top level considered?

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