Array subclassing, .map and iterables (Re: Jan 30 TC39 Meeting Notes)

[Rick Waldron]

On Sun, Feb 10, 2013 at 3:04 PM, Tab Atkins Jr. <jackalmage at gmail.com>wrote:

> On Sun, Feb 10, 2013 at 11:18 AM, Rick Waldron <waldron.rick at gmail.com>
> wrote:
> > (Assuming a future where the DOM's NodeList inherits from Array)
> >
> > How would you produce a NodeList from an arbitrary array of strings?
> >
> >   NodeList.from( [ "div", "span", "p" ], nodeName =>
> > document.createElement(nodeName) );
> >
> > Because...
> >
> >   NodeList.from( strings );
> >
> > Would try to make a NodeList, but with items that of a type that it
> > disallows, meaning:
> >
> >   NodeList.from( strings ).map( nodeName =>
> document.createElement(nodeName)
> > );
> >
> > Would call .map() on an empty NodeList, since the string value items had
> > been rejected. Of course, you might argue that I could just call it like:
> >
> >   NodeList.from( [ "div", "span", "p" ].map(nodeName =>
> > document.createElement(nodeName)) );
> >
> > ...But the "arraylike" or "iterable" might not have a .map() method of
> its
> > own, which will cause issues if I'm in a JS-target transpilation
> scenario...
>
> From what I've seen in the examples in this topic so far, it looks
> like Array#from takes a second optional argument, which is a function
> that you map the iterable elements through first, before giving them
> to the constructor.
>

Yes, and I said just as much (not same words) further down the thread.


> So, you would write:
>
> NodeList.from( ["div", "span", "p"],
> (nodeName)=>document.createElement(nodeName) );
>

This is exactly the same as the very first solution I offered:

> (Assuming a future where the DOM's NodeList inherits from Array)

> How would you produce a NodeList from an arbitrary array of strings?

>  NodeList.from( [ "div", "span", "p" ], nodeName =>
document.createElement(nodeName) );


Rick



> ~TJ
>
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