FWIW, performance seems to be equivalent: http://jsperf.com/typeof-vs-undefined-check/39
Chris https://chrismatic.io/ > On Nov 30, 2015, at 1:01 PM, Geoffrey Garen <gga...@apple.com> wrote: > > For the time being, I like “x === undefined”. > > Long term, I’d like us to switch to “x === @undefined”. > > We use @ to indicate reserved words in built-ins. Currently, “@undefined" > does not exist, but the built-in compiler magically transforms “undefined” a > safe reserved word. > > The typeof and void 0 code should be fast, but I find it obtuse. > > Geoff > >> On Nov 30, 2015, at 11:39 AM, Filip Pizlo <fpi...@apple.com> wrote: >> >> I’ve also been guilty of: >> >> if (xxx === void 0) >> >> This is slightly better than saying “undefined”, since that’s not actually a >> reserved word. >> >> I believe that all of these should perform the same. We should pick one >> based on what looks nicest and what has the most clear semantics. >> >> -Filip >> >> >> >>> On Nov 30, 2015, at 11:37 AM, Darin Adler <da...@apple.com> wrote: >>> >>> I see the following in some code: >>> >>> if (xxx === undefined) >>> >>> And I see the following in some other code: >>> >>> if (typeof xxx == “undefined”) >>> >>> or >>> >>> if (typeof xxx === “undefined”) >>> >>> Is one preferred over the other, style-wise? Is one more efficient than the >>> other? >>> >>> — Darin >>> _______________________________________________ >>> webkit-dev mailing list >>> webkit-dev@lists.webkit.org >>> https://lists.webkit.org/mailman/listinfo/webkit-dev >> >> _______________________________________________ >> webkit-dev mailing list >> webkit-dev@lists.webkit.org >> https://lists.webkit.org/mailman/listinfo/webkit-dev > > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
