fail-fast object destructuring

Brendan Eich brendan at
Tue Jul 10 07:40:10 PDT 2012

Russell Leggett wrote:
> Another thing that I was also thinking is that it might look a little 
> nicer if the ? was a post-fix instead of a pre-fix.
>     let {first, last, company?} = contact;
> I might be missing why this wouldn't work out, but it aesthetically 
> just looks right to me. It looks like the regex operator, and is also 
> obviously the position it would be in english.

We have to parse LHS-of-assignment patterns using the Expression cover 
grammar, so this does not work in general due to ?:.

If we parse only in binding contexts (let, const, var on the left, or 
formal params and catch clauses), then we could use a different pattern 
grammar. Worth breaking uniformity with assignment expressions?


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