On Apr 13, 2012, at 9:50 AM, Russell Leggett wrote:
>
> I'd write it:
>
> function fadeToggle(...args){
> if(visible){
> fadeOut(...args);
> }else{
> fadeIn(...args);
> }
> }
>
> If you don't care about the the actual argument values are just passing them
> on that's how you should do it.
>
> Ok, sure, but in an equally likely case, only one of the arguments is a pass
> through, should you still use ...args for one thing just to distinguish? What
> about other case like objects with optional properties
> fadeIn(config.duration)?
One of the nice things about ES6 is that we have destructuring and
default/rest arguments. The defaulting semantics of destructuring binding is
currently exactly the same (they use the same semantic rules) as formal
parameter binding. that means you can almost[*] always replace:
function f(<formals>) { ...
}
with
function f(...args) {
let [<formals>] = args;
...
}
If you want to treat some argument one way in certain circumstances and another
way in other circumstances all you have to do is do one or more manual
destructurings such as above.
[*] It's "almost" because slightly different shadowing rules are used when
processing default value expression in the formals parameters position. Such
differences can be avoid if you are careful in your name selection.
>
> I just don't understand why someone who wanted to be able to distinguish
> between missing and undefined would really need the extra convenience of
> default parameters. What are they going to default to - undefined? Meanwhile,
> the rest of the people that probably could use it all the time to replace
> their foo = foo || "default" code have to keep it around. I understand what
> you're saying in principle. There is a certain amount of purity and
> correctness to it, I just don't think its practical.
function f(foo="default") {}
if not semantically the same as
function f(foo) {foo == foo || "default"}
consider
f(null), f(false), f(0), f(NaN), f("")
Allen
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