*> What am I missing?* Nothing with respect to function arguments, AFAICT.
But to beat the dead-cognitive-overhead horse again, the rules around ACI (Automatic Comma Insertion) appear to require too many exceptions. We've already covered: - ACI doesn't apply at all between variable declarations - ACI has exceptions around getter/setter properties in object literals. I hadn't thought of these before, but there's also: - ACI would need exceptions in object and array literals following yield in generator functions. - ACI would need exceptions in object and array literals following await in async functions. I would wager this isn't an exhaustive list yet, either. To be clear, these aren't exceptions in the grammar itself (the ASI-style "insert comma if next token would generate a syntax error" is sufficient to handle all of these cases), but they *are* exceptions that developers and tooling would need to hold onto, and IMHO, relegate the purported readability improvements. On Wed, Sep 13, 2017 at 1:55 PM, Naveen Chawla <[email protected]> wrote: > `x` <whitespace> `[y]` would be invalid syntax, right? > So > ```js > x > [y] > ``` > would automatically insert a comma in the case of a function call > arguments list, right? > > That's exactly what would be desired. What am I missing? > > On Wed, 13 Sep 2017 at 20:52 Boris Zbarsky <[email protected]> wrote: > >> On 9/13/17 9:57 AM, Naveen Chawla wrote: >> > By this behaviour (a modification to the initial "complete statement >> > produces comma" version of this proposal), everything would work >> > perfectly, no? >> >> If by "perfectly" you mean "have hard-to-predict somewhat nonlocal >> behavior that makes any code relying on this a hard-to-read footgun", >> then the answer might be "yes". For pretty much any other definition of >> "perfectly", I'm fairly sure the answer is "no". >> >> > Great to hear those counter-examples as I don't know enough about ASI, >> >> Still in the context of ASI, here are some examples of why ASI is a bad >> idea: >> >> 1) What does this return? >> >> function f() { >> return >> 5; >> } >> >> 2) What does this alert? >> >> var str = "hello"; >> var x = str >> [x].forEach(() => alert(x)) >> >> Now back to automatic comma insertion... In your example: >> >> function doStuff( >> x >> y >> z >> ){ >> } >> >> if someone changes doStuff to take an array as the second arg and you >> modify the call as: >> >> function doStuff( >> x >> [y] >> z >> ){ >> } >> >> suddenly you need to insert a comma after the "x" to preserve the right >> semantics, no? This is not terribly intuitive or obvious. It gets even >> worse in a situation like this: >> >> function doStuff( >> x >> /* The next argument is an array for good reasons that we >> will now expound on in a long comment, etc, etc */ >> [y] >> ){ >> } >> >> Quick, tell me without testing this or looking at the spec for a while >> whether this is a valid call to doStuff, with one argument, or a syntax >> error that would trigger comma insertion. >> >> But more generally, if you just use your favorite search engine on the >> phrase "automatic semicolon insertion", you will get a slew of articles >> explaining the pitfalls. >> >> -Boris >> > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > > -- Jeremy Martin 661.312.3853 @jmar777 <https://twitter.com/jmar777> / @j <https://stream.live/j>
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