On 25 June 2012 17:17, David Herman <[email protected]> wrote:
> Implicit coercions suck, and IMO it would be better if destructuring didn't
> add new ones to JS. In the current draft spec, I believe if you match an
> object destructuring pattern against a non-object or an object that doesn't
> have one or more of the properties, it quietly proceeds -- masking what is
> quite likely an error:
>
> var { foo, bar } = getFooAndBar();
>
> If getFooAndBar() doesn't produce an object with foo and bar properties,
> there's probably something going wrong! And most of the time when you do want
> to be forgiving (say, in a function signature, or when reading a
> configuration file), you have a specific default value you want to provide,
> which can be specified with the default syntax:
>
> var { foo = defaultFooValue, bar = defaultBarValue } = getFooAndBar();
>
> I'd like to propose the following changes:
>
> (a) Throw when matching null, undefined, booleans, or strings against an
> object pattern. (I don't propose throwing when matching a string against an
> array pattern, however, since strings behave structurally like read-only
> arrays.)
>
> (b) Allow a shorthand "?" prefix for properties in an object destructuring
> pattern. This is simply shorthand for defaulting to undefined. IOW, the
> following are all equivalent:
>
> var { ?foo } = getFoo();
> var { foo = undefined } = getFoo();
> var { foo: foo = undefined } = getFoo();
> var { ?foo: foo } = getFoo();
>
> Note, however, that (b) is not strictly necessary to get the fail-soft
> behavior. You can always write the explicit default. But it makes it
> considerably more convenient to get the fail-soft behavior when you want it
> -- only one character more expensive than fail-fast.
+10^20, although you don't say that "let {foo} = {}" should throw as
well -- but your (b) doesn't seem to be motivated without proposing
that.
/Andreas
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