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From: Rolf Niepraschk <Rolf.Niepraschk@gmx.de>
Newsgroups: comp.lang.javascript
Subject: Re: Iterating through an array (special syntax)
Date: Tue, 17 Oct 2017 18:46:55 +0200
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Xref: csiph.com comp.lang.javascript:34122

Am 17.10.2017 um 15:19 schrieb Michael Haufe (TNO):
...
> 
> This can be a bit more efficient by eliminating the intermediate object and such, but I prefer clarity in this case as we don't know the larger architectural requirement:
> 
> <script>
> function foo(xs) {
>    return {
>      oldItems: xs,
>      newItems: xs.map(x => x * 2),
>      each: function(fnUnzip){
>        xs.forEach((x,i) => fnUnzip(x, this.newItems[i]))
>      }
>    }
> }
> 
> foo([1,2,3,4]).each((oldItem,newItem) => {
>    console.log(`oldItem: ${oldItem} newItem: ${newItem}`)
> })
> </script>
> 
> This is newer than ES5 so compile/translate as necessary for your target environment.
> 

This solution is very helpful and I can use modern browsers and a recent 
nodejs version. Many Thanks.

But one Problem remains. How must be the function modified if the array 
is generated in an asynchronous way? For example:

//--------------------------------------------------------
function foo() {
   setTimeout(function() {
     var arr = [1,2,3,4];
     // ???
   }, 500);
}

foo().each((oldItem,newItem) => {
    console.log(`oldItem: ${oldItem} newItem: ${newItem}`)
})
//--------------------------------------------------------

...Rolf