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Similarly to:
`var [,x,,y] = [1,2,3,4,5,6];`
I think it could be interesting to let a field empty in function arguments
`[1,2,3,4].map( (,i) => i )`, `Array.from({length:10}, (,i) => i )`
`function test(a,,b) { }`
(but that would alter the current parsing, that doesn't allow it)
Currently I often use `_` as a way to mark ignored fields, but when there are more than 1 you need another identifier. A standard way would be interesting rather _______________________________________________
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Eliding array elements is not "similar" to eliding function formal parameters. The latter is extremely rare, hardly readable, confusing, bug-prone, and unnecessary because there is already a "standard way" which is to use any old parameter name you want:
```js function foo(UNUSED1, UNUSED2, x) ````
Most linters will not complain, or there are ways to shut them up if they do.
If you want to throw away an argument, just throw it away.
```js function skipFirstParam(fn) { return ((first, ...args) => fn(...args)); }
`[1,2,3,4].map(skipFirstParam(i => i));
```
Or use Renki's solution.
Bob
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``` function fn(...[a, b, c, ...rest]){} ``` is mostly no different than ``` function fn(...args){ let [a, b, c, ...rest] = args;
}
```
Not that I think this example is particularly readable :) _______________________________________________
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You could stop with "rare"; having to make up unused names is an obvious smell in comparison.
```js foo(UNUSED1, UNUSED2, x)
foo(_, __, x)
foo(...[,, x]) ```
The latter is shorter and more explicit and would not be any more confusing if it became common. _______________________________________________
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Since functions arguments is an array under the hood, they could 'more behave the same'
Both function arguments and arrays accept spreading: [1, 2, ...args] and fn(1, 2, ...args)
a function definition like (,i) => {}, would be the equivalent of var [,i] = arguments
an invocation fn(,,i) would be the equivalent of [,,i]
It's possible with (...[,i]) => {}, (_,i)=>{} like Renki said, but slightly less simply
Are there possible issues with that 'extension' of function syntax?
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Just bumping this up
Calling `foo(1)` where foo is defined with 3 arguments, lets the 2 others undefined, this behavior is already a bit magic and similar to the behavior of an array, so I still think foo(a,,b,,,c) should be like foo(...[a,,b,,,c])
Other example: ``` var m=new Map([[1], [2,], [3,7]]) // Map {1 => undefined, 2 => undefined, 3 => 7} // here commas fantasies are allowed in arrays m.set(3) // Map {1 => undefined, 2 => undefined, 3 => undefined} // setting implicitely value as undefined m.set(3, ) // not allowed, which should be m.set(...[3,])
```
and again, it would help for callbacks too, `something( ( , , thirdArg) => {} )`
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For what it's worth, elided array elements aren't available in strict mode (they're a syntax error), and it's not likely anyone is going to want to add a new sloppy mode only feature. Plus, it's not easy to tell at a glance if it's a typo or intentional. `Math.min(x,,y)` is a likely error, but a syntax error is much more informative than `NaN` or a very odd `undefined`. I don't see the point of not making it explicit.
Just bumping this up
Calling `foo(1)` where foo is defined with 3 arguments, lets the 2 others undefined, this behavior is already a bit magic and similar to the behavior of an array, so I still think foo(a,,b,,,c) should be like foo(...[a,,b,,,c])
Other example: ``` var m=new Map([[1], [2,], [3,7]]) // Map {1 => undefined, 2 => undefined, 3 => 7} // here commas fantasies are allowed in arrays m.set(3) // Map {1 => undefined, 2 => undefined, 3 => undefined} // setting implicitely value as undefined m.set(3, ) // not allowed, which should be m.set(...[3,])
```
and again, it would help for callbacks too, `something( ( , , thirdArg) => {} )`
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Okay. I'll admit I'm wrong here. I misremembered. I knew they were more of a legacy thing, I just didn't know they were available in strict mode.
For what it's worth, elided array elements aren't available in strict mode
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What if you could use a `.` as a wildcard? I don’t think it would conflict with existing syntax, and it would avoid binding a usable identifier. It would be more obvious than nothing between the commas.
Just bumping this up
Calling `foo(1)` where foo is defined with 3 arguments, lets the 2 others undefined, this behavior is already a bit magic and similar to the behavior of an array, so I still think foo(a,,b,,,c) should be like foo(...[a,,b,,,c])
Other example: ``` var m=new Map([[1], [2,], [3,7]]) // Map {1 => undefined, 2 => undefined, 3 => 7} // here commas fantasies are allowed in arrays m.set(3) // Map {1 => undefined, 2 => undefined, 3 => undefined} // setting implicitely value as undefined m.set(3, ) // not allowed, which should be m.set(...[3,])
```
and again, it would help for callbacks too, `something( ( , , thirdArg) => {} )`
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Confused by this thread.
> What if you could use a `.` as a wildcard?
You can already use `_` or anything you want, as was already pointed out in early iterations of this idea.
> it would avoid binding a usable identifier.
What is the problem with that?
What is the problem that this proposal is trying to solve? Any chance we could move on?
Bob
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> Confused by this thread.
It's quite simple though, _ would be a useless allocated variable, you an't have more than 1, ...
> What is the problem that this proposal is trying to solve?
ignoring/skipping argument in functions declarations (indeed the invocations could be let apart)
> `Math.min(x,,y)`
yes this kind of thing would give NaN, that's why you can `Math.min(x, , y)` write it with more spaces to avoid a typo mistake, indeed you could still have like `Math.min(x, /*y (no longer used)*/ , z)` would. Like said above, I realize the function invocations are sensible.
So, it would be only for function declarations
`div.addEventListener('click', () => { } )` says to skip all arguments, and you've your callback scope is free of any additional vars
`arr.forEach( x => { } )` says to only consider first argument, others are skipped, and not in scope
`Array.from({length: 19}, (, i) => i )` would be similar for the second argument, similarly to array destructuring. It's not just for saving one character, that's really not the matter, it's for standardizing this way, because some people use `_`, some don't, ....
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ignoring/skipping argument in functions declarations (indeed the invocations could be let apart)
I am of the opinion that this is not a problem that needs to be solved at the language standardization level. The commas (or really any separator) for "skipping" a parameter looks like a mistake and is unintuitive (it's certainly not obvious to me what its intent is had I seen it without the context of this thread).
This seems like a problem solved with better coding practices. I typically make required parameters first and then any optional ones in a separate, single parameter called options. Callbacks can be done with chaining / promises / I fmake them required / etc. Skipping callbacks usually isn't a good idea. We could talk all day about who's coding practice is better than who's but ultimately this problem should be solved by developing / adopting good coding practices.
(Honestly I'm not a fan of the skipping in arrays either but considering it's an array I feel like it's at least a magnitude less confusing than doing it with function parameters) _______________________________________________
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If you're talking about ignored function parameters in a declaration or expression, much like `_` in several functional languages (like Haskell and Scala), I could see value in that. I'd prefer an explicit token for that, though, something like this:
```js
// ImmutableJS: convert map to list, only
// keeping values with integer keys
map
.filter((*, key) => typeof key === "number" && key % 1 === 0)
.toList()
```
ignoring/skipping argument in functions declarations (indeed the invocations could be let apart)
I am of the opinion that this is not a problem that needs to be solved at the language standardization level. The commas (or really any separator) for "skipping" a parameter looks like a mistake and is unintuitive (it's certainly not obvious to me what its intent is had I seen it without the context of this thread).
This seems like a problem solved with better coding practices. I typically make required parameters first and then any optional ones in a separate, single parameter called options. Callbacks can be done with chaining / promises / I fmake them required / etc. Skipping callbacks usually isn't a good idea. We could talk all day about who's coding practice is better than who's but ultimately this problem should be solved by developing / adopting good coding practices.
(Honestly I'm not a fan of the skipping in arrays either but considering it's an array I feel like it's at least a magnitude less confusing than doing it with function parameters)
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