Best test for undefined?
in [JavaScript]
|
From: Stefan Weiss on 11 May 2010 20:09 On 11/05/10 19:34, Dr J R Stockton wrote: > In comp.lang.javascript message <ab37b500-1b97-450c-9498-badd643ac361(a)j3 > 5g2000yqm.googlegroups.com>, Sun, 9 May 2010 20:02:32, nick > <nick___(a)fastmail.fm> posted: >>What's the "best" way to determine if a variable is defined? > > I don't recall any problem in testing X for the value undefined by using > > var U > // ... > if (X==U) ... > > although one must remember not to define U. .... and to use the strict comparison operator. > It was a design fault to give the language an undefined type and an > undefined value, since it is then unnecessarily difficult to talk about > it in English. Instead, non-words should have been used - "taghairm" > would nearly serve; "trygdyl" would do. All who know English reasonably > well will understand that those are not English words. > > One cannot test directly whether the variable 'akwidukt' has been > declared, since a simple reference to it will give an error. But > 'window.akwidukt' is merely 'undefined' if 'akwidukt' has not been > defined. Those are perfectly cromulent words which could embiggen our awkward language. You should tell the Harmony people about your idea. -- kwyjibo
From: "Michael Haufe ("TNO")" on 11 May 2010 21:34 On May 9, 10:02 pm, nick <nick...(a)fastmail.fm> wrote: > What's the "best" way to determine if a variable is defined? foo in this //throws when foo is undefined
From: Ry Nohryb on 12 May 2010 01:57 On May 12, 3:34 am, "Michael Haufe (\"TNO\")" <t...(a)thenewobjective.com> wrote: > On May 9, 10:02 pm, nick <nick...(a)fastmail.fm> wrote: > > > What's the "best" way to determine if a variable is defined? > > foo in this //throws when foo is undefined "foo" in this doesn't. -- Jorge.
From: Dr J R Stockton on 13 May 2010 12:00 In comp.lang.javascript message <5dmdnU-R8ZcDbHTWnZ2dnUVZ8ludnZ2d(a)gigane ws.com>, Wed, 12 May 2010 02:09:01, Stefan Weiss <krewecherl(a)gmail.com> posted: >On 11/05/10 19:34, Dr J R Stockton wrote: >> In comp.lang.javascript message <ab37b500-1b97-450c-9498-badd643ac361(a)j3 >> 5g2000yqm.googlegroups.com>, Sun, 9 May 2010 20:02:32, nick >> <nick___(a)fastmail.fm> posted: >>>What's the "best" way to determine if a variable is defined? >> >> I don't recall any problem in testing X for the value undefined by using >> >> var U >> // ... >> if (X==U) ... >> >> although one must remember not to define U. > >... and to use the strict comparison operator. Is that needed if X cannot be null ? -- (c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME. Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links; Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
From: Stefan Weiss on 17 May 2010 13:38
On 13/05/10 18:00, Dr J R Stockton wrote: > In comp.lang.javascript message <5dmdnU-R8ZcDbHTWnZ2dnUVZ8ludnZ2d(a)gigane > ws.com>, Wed, 12 May 2010 02:09:01, Stefan Weiss <krewecherl(a)gmail.com> > posted: > >>On 11/05/10 19:34, Dr J R Stockton wrote: >>> In comp.lang.javascript message <ab37b500-1b97-450c-9498-badd643ac361(a)j3 >>> 5g2000yqm.googlegroups.com>, Sun, 9 May 2010 20:02:32, nick >>> <nick___(a)fastmail.fm> posted: >>>>What's the "best" way to determine if a variable is defined? >>> >>> I don't recall any problem in testing X for the value undefined by using >>> >>> var U >>> // ... >>> if (X==U) ... >>> >>> although one must remember not to define U. >> >>... and to use the strict comparison operator. > > Is that needed if X cannot be null ? No, but that wasn't mentioned anywhere by the OP. -- stefan |