Toplevel 'let' binding can be left permanently uninitialized after an error

Brian Genisio briangenisio at gmail.com
Tue Sep 30 11:08:55 PDT 2014


FYI, you can also see this behavior in Node.js (v0.11.14)

node --harmony --strict-mode

On Tue, Sep 30, 2014 at 1:24 PM, Rick Waldron <waldron.rick at gmail.com>
wrote:

>
>
> On Tue, Sep 30, 2014 at 1:08 PM, Allen Wirfs-Brock <allen at wirfs-brock.com>
> wrote:
>
>>
>> On Sep 30, 2014, at 10:00 AM, Rick Waldron wrote:
>>
>>
>> My original response questions were poorly asked. I understand the TDZ
>> semantics, but I couldn't reproduce anything meaningful from your original
>> example, because I don't have the SpiderMonkey build that includes the let
>> updates (presumably Nightly doesn't either, because none of these can be
>> reproduced there). I'm trying to understand when/where/why/how the original
>> example could happen and what the potential consequences are in terms of
>> practical application.
>>
>>
>> Also, note that IE11 apparently implements the ES6 let semantics so it
>> may be useful to look at its experience in this regard.
>>
>
> As a Mac user, I completely forgot about this. Using Browserstack.com, I
> was able to reproduce the original example's behavior by running a script
> and then attempting to access or assign to x from the console. The behavior
> I observe is exactly what I expect. I'm still unable to provide any further
> insight regarding Jason's original comments and practical implications of
> reported behavior.
>
>   "That by itself isn't necessarily a problem. I've never written a web
>   page where I wanted to recover after a toplevel script threw an
>   exception (or timed out)."
>
> I agree with the first assertion for the same reason stated.
>
> Rick
>
>
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