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? 2016年9月14日(水) 7:51 Dan Peddle <[email protected]>: > An alternative to the block which you ended up with is to extract that > logic to a function, which provides something which can be tested too. > Possibly overkill for oneliners like this though. > > However, writing a lot of code like this myself (get a value, if it's > truthy do something, else do other), that's a nice idea for an extension > that doesn't add extra variable bindings to the containing scope. > > On Tue, Sep 13, 2016 at 2:32 AM, Danielle McLean <[email protected]> > wrote: > >> In current ECMAScript, it is legal to place a variable declaration inside >> the >> initialiser of a `for` loop, as well as to declare the variable used by a >> `for...in` or `for...of` loop within the declaring expression: >> >> for (let i = 0; i < 5; ++i) console.log(i); >> for (let item of collection) process(item); >> >> When this syntax is used with `let` or `const`, the resulting variable is >> scoped to the loop and is not visible to the rest of the surrounding >> block. >> >> I propose that this syntax be extended, making it legal to place a >> variable >> declaration within the condition of an `if` or `while` statement. Any >> truthy >> value will cause the `if` block to run or `while` loop to repeat, as >> usual - >> the advantage is that the particular truthy value is bound to a variable >> and >> can be used inside the conditional block. For example, here is the >> situation >> that prompted my writing this proposal: >> >> if (const oldValue = _.get(object, 'some.long.path')) { >> object.some.long.path = transform(oldValue); >> } >> >> As with the existing behaviour of declarations inside `for`, variables >> declared >> using `let` or `const` would be scoped to the individual `if` or `while` >> statement, rather than the containing block. In other words, the above >> syntax >> would be equivalent to the following currently-valid form I ended up >> writing: >> >> { >> const oldValue = _.get(object, 'some.long.path'); >> if (oldValue) object.some.long.path = transform(oldValue); >> } >> >> Another use case which C aficianados might recognise: >> >> while (const c = getchar()) { >> process(c); >> } >> >> This syntax is already legal in C++, although not in C - in general this >> support is known as "anaphoric if", as it allows the body of the >> statement to >> refer back to the condition value. It's especially helpful in languages >> with >> truthiness, which ECMAScript has, as it allows access to the *specific* >> truthy >> value without further finagling. >> >> Thoughts? >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> > > > > -- > > Dan Peddle > *tel*: +49 157 3918 2066 > *email*: [email protected] > *www*: http://flarework.com > *in*: http://pt.linkedin.com/in/danpeddle > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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