clearing a global array
in [JavaScript]
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From: MikeJ on 27 Apr 2010 18:05 I tried GlobalArray.length = 0; and it worked... but is it legit? Thanks Mike On Tue, 27 Apr 2010 14:17:58 -0700 (PDT), Sean Kinsey <okinsey(a)gmail.com> wrote: >On Apr 27, 11:05�pm, MikeJ <no_spam_ple...(a)nothere.com> wrote: >> Need to know how to clear a global array so Array.length will = 0 >> (meaning no indexes). Cant find the information in the book. >> Thanks >> Mike > >If the Array is only referenced by a single global variable then the >easiest way is to just replace the reference to with that of a new >Array >var globalArray = [foo, bar]; > >//reset >globalArray = []; > >Alternatively you can use splice which adds/removes elements from the >array >globalArray.splice(0, globalArray.length - 1); >(not sure if '- 1' is needed here)
From: MikeJ on 27 Apr 2010 18:12 Posted before I re-checked replies.. Thanks Mike On Tue, 27 Apr 2010 23:22:27 +0200, Stefan Weiss <krewecherl(a)gmail.com> wrote: >On 27/04/10 23:05, MikeJ wrote: >> Need to know how to clear a global array so Array.length will = 0 >> (meaning no indexes). Cant find the information in the book. > >To truncate an array so that arr.length = 0, you need to write > > arr.length = 0; > >I know, weird and unexpected syntax, but there it is ;)
From: Sean Kinsey on 27 Apr 2010 18:11 On Apr 27, 11:27 pm, Stefan Weiss <krewech...(a)gmail.com> wrote: > On 27/04/10 23:17, Sean Kinsey wrote: > > > On Apr 27, 11:05 pm, MikeJ <no_spam_ple...(a)nothere.com> wrote: > >> Need to know how to clear a global array so Array.length will = 0 > >> (meaning no indexes). Cant find the information in the book. > >> Thanks > >> Mike > > > If the Array is only referenced by a single global variable then the > > easiest way is to just replace the reference to with that of a new > > Array > > var globalArray = [foo, bar]; > > > //reset > > globalArray = []; > > Strictly speaking, that doesn't "clear" the array, it just assigns the a > new empty Array to the variable globalArray: > > var arr = [1, 2]; > var alias = arr; > > arr = []; > print alias.length; // 2 -- whoops! Maybe you should read my statement again, especially the part with "..is only referenced by a single global variable.."
From: Stefan Weiss on 27 Apr 2010 18:46 On 28/04/10 00:11, Sean Kinsey wrote: > On Apr 27, 11:27 pm, Stefan Weiss <krewech...(a)gmail.com> wrote: >> Strictly speaking, that doesn't "clear" the array, it just assigns the a >> new empty Array to the variable globalArray: >> >> var arr = [1, 2]; >> var alias = arr; >> >> arr = []; >> print alias.length; // 2 -- whoops! > > Maybe you should read my statement again, especially the part with > "..is only referenced by a single global variable.." My example was just an attempt to illustrate the conceptual difference between clearing an array (see subject) and replacing it with a new one. If there's only a single reference, there won't be any practical difference, of course. In that context, I would tend to prefer 'arr = []', too. -- stefan
From: Richard Cornford on 27 Apr 2010 21:04
MikeJ wrote: > Sean Kinsey wrote: > I tried GlobalArray.length = 0; > and it worked... but is it legit? <snip - misplaced, and redundant quote> Yes it is legitimate. Array instances have a special (array specific) version of the internal [[Put]] method that may modify the array's - length - property if the property name to which a value is assigned qualifies as an 'array index' and may delete 'array index' properties of the array object when values are assigned to the array's - length - property. In the latter case, when a value is assigned to - length - any 'array index' properties that are greater than or equal to the value assigned are deleted. Thus assign zero to - length - and all 'array index' properties of the array object are deleted. (This special [[Put]] behaviour maintains/enforces the relationship between the array's - length - property and its 'array index' properties such that the - length - is always at least one greater than the largest 'array index' property.) Richard. |