excluding features from sloppy mode

Brendan Eich brendan at mozilla.com
Sun Dec 30 11:53:27 PST 2012

Brandon Benvie wrote:
> On Sunday, December 30, 2012, Mark S. Miller wrote:
>     In the short term, while people are making the transition, the rule
>     would be stated as above “If you want the new stuff, turn on strict
>     mode or wrap a module around it.” Later, once ES6 is everywhere, it
>     would instead be stated as "Turn on strict mode or code in a module in
>     order to code in JavaScript. If you don't, you'll be coding instead in
>     an insane JavaScript fossil that exists merely for compatibility with
>     old ES3 code. No one even understands its scoping rules."
> This is a very attractive idea. It seems like it is is the simplest of 
> all possible stories to learn, teach, use, specify, and implement.

Come on, you guys. Your own biases are on parade here.

First, the scoping rules of sloppy mode are know and used, some even 
advocate using them in full (yes, even 'with').

Strict mode does tame *most* of the scoping crazy, I like it. But it 
does not make

* free variables an early error;

* implicit conversions, e.g. random string to 0 or NaN, or anything that 
can wreck your == day, an early error;

* fetching a missing property and getting undefined, which flows miles 
downstream before being dereferenced, any kind of prompt error that 
blames the missing property and its base object.

So exaggerating the "insane" sloppy mode's flaws both overdoes it in the 
face of lots of legacy and many developers who must deal with it (some 
of whom like it), *and* oversells strict mode as fixing the above 
bulleted items.

All this happy talk about teaching slogans smells like propaganda. It 
won't work. It is still overcomplicated and hard to use compared to "new 
syntax, just use it". And the exaggerations and overstatements will bite 
back, as badly as or worse than any 'let [x] = y' breaking change.


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