While I like the idea of making it simpler to restrict the scope of variables, currently a reigning best practice is to never do assignment in conditionals, since it can be an easy typo from `==` or `===`, and because it conflates assignment with expression truthiness, harming readability.
This seems like it runs afoul of the latter, certainly, and I haven't yet convinced myself whether it creates typo hazards (I'm thinking no, but wanted to bring it up just in case). On Wed, Sep 14, 2016 at 3:14 AM, Danielle McLean <[email protected]> wrote: > On 14 September 2016 at 17:58:24, Viktor Kronvall > ([email protected](mailto:[email protected])) wrote: > > > Does this really need new semantic interpretation of the syntax? Using > the `Array.prototype` methods `.forEach` and `.map` already mitigates this > problem as far as I can tell by having a different bound variable (argument > in this case) for each call. > > > > I agree that the behavior may be non-intuitive if you have a background > coming from Java or C++ but the implications would be quite far-reaching > and the backward compatibility with previous versions would be difficult to > handle. Wouldn't this require a new 'use strict'-like mode? > > No, adding anaphoric if as I have described it will require neither > new semantic interpretation of the syntax nor a new strictness > directive. Currently, it is a syntax error to write a variable > declaration within an `if` or `while` condition, so there is no valid > code which contains the proposed syntax. > > Also note that under this proposal, declarations made using the `var` > keyword would still be hoisted to function scope, *not* scoped to the > body associated with the condition - i.e., there would be no semantic > difference whatsoever between the following two snippets: > > if (var stuff = some.cool(expression)) doThings(stuff); > // equivalent to > var stuff; > if (stuff = some.cool(expression)) doThings(stuff); > > Only declarations made with the newer `let` and `const` keywords, > which are never hoisted to function scope anyway, would be narrowly > scoped to the condition and its body. > > if (let stuff = expr) doThings(stuff); > // equivalent to > { > let stuff = expr; > if (stuff) doThings(stuff); > } > > (An aside: as the last example demonstrates, the `if` or `while` > statement body should not need braces to isolate the scope in this > way. This is consistent with the current behaviour for declarations in > loops.) > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
_______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
