Bug: String.prototype.endsWith

[Rick Waldron]

That jsperf is too noisy to actually be measuring the performance of
anything. If you want to test the performance of just the logic in question
- then that should be all that exists.

See: http://jsperf.com/endwithlogic

>From a web dev perspective... fallback definitions should always try to
minimize the number of _other_ function calls they make.


Rick


On Fri, Sep 23, 2011 at 5:11 PM, Xavier MONTILLET
<xavierm02.net at gmail.com>wrote:

> [Nope, wasn't deliberate]
>
> I tested and both are as fast apparently but doing it the "hard" way
> seems slow. But maybe that's because I didn't do it properly.
>
> And a function isAt could be useful. But it needs another name :-*
>
>
> http://jsperf.com/endswith
>
> On Fri, Sep 23, 2011 at 10:22 PM, Axel Rauschmayer <axel at rauschma.de>
> wrote:
> > [Was not-cc-ing es-discuss deliberate? Feel free to forward this email if
> it wasn’t.]
> >
> > Creating a substring isn’t very efficient, either. But I get your point:
> Why search the whole string, when it is enough to check a single position?
> >
> > A better solution might be to create a helper method
> >    String.prototype.isAt(substr, pos)
> > that returns true if substr is found at position pos in "this".
> >
> > This helper method could be used to implement endsWith and startsWith.
> >
> > However, I doubt that the goal for the code was efficiency.
> >
> > On Sep 23, 2011, at 22:12 , Xavier MONTILLET wrote:
> >
> >> Why doesn't it simply do
> >>
> >> String.prototype.endsWith = function(s) {
> >>    return this.substring( this.length - s.length ) === String(s);
> >> };
> >>
> >> ?
> >>
> >> I mean lastIndexOf must be much slower...
> >>
> >> On Fri, Sep 23, 2011 at 9:18 PM, Axel Rauschmayer <axel at rauschma.de>
> wrote:
> >>> http://wiki.ecmascript.org/doku.php?id=harmony:string_extras
> >>> I’ve found a small bug:
> >>>
> >>> String.prototype.endsWith = function(s) {
> >>>
> >>>    var t = String(s);
> >>>    return this.lastIndexOf(t) === this.length - t.length;
> >>> };
> >>>
> >>> Interaction:
> >>>
> >>>> "".endsWith("/")
> >>> true
> >>>> "#".endsWith("//")
> >>> true
> >>>> "##".endsWith("///")
> >>> true
> >>>
> >>> Fix (e.g.):
> >>>
> >>> String.prototype.endsWith = function(s) {
> >>>    var t = String(s);
> >>>
> >>>    var index = this.lastIndexOf(t)
> >>>    return index >= 0 && index === this.length - t.length;
> >>> };
> >>>
> >>> --
> >>> Dr. Axel Rauschmayer
> >>> axel at rauschma.de
> >>> twitter.com/rauschma
> >>> home: rauschma.de
> >>> blog: 2ality.com
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> es-discuss mailing list
> >>> es-discuss at mozilla.org
> >>> https://mail.mozilla.org/listinfo/es-discuss
> >>>
> >>>
> >>
> >
> > --
> > Dr. Axel Rauschmayer
> >
> > axel at rauschma.de
> > twitter.com/rauschma
> >
> > home: rauschma.de
> > blog: 2ality.com
> >
> >
> >
> >
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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