Is there a sweet way to init an array if not already initilized? Currently the code looks something like:
if (!obj) var obj = [];
obj.push({});
cool would be something like var obj = (obj || []).push({}), but that does not work :-(
views:
115answers:
4
+8
A:
var obj = (obj || []).push({}) doesn't work because push returns the new length of the array. For a new object, it will create obj with value of 1. For an existing object it might raise an error - if obj is a number, it does not have a push function.
You should do OK with:
var obj = obj || [];
obj.push({});
Kobi
2010-09-14 13:13:58
gnarf
2010-09-14 13:59:15
@gnarf - Interesting idea. If I understand correctly, the line should still start with `var obj = `.
Kobi
2010-09-14 14:11:18
except implicitly, `obj` *should* always be undefined in this case, which makes the `(obj || [])` just `[]`
gnarf
2010-09-14 13:53:30
No it won't. `var obj;` won't set `obj` to `undefined` if it was `defined` before.
RoToRa
2010-09-14 14:23:49
Unless you are using `var obj` twice in the same scope, which just seems like a waste of the `var` to me...
gnarf
2010-09-14 16:00:23
I fear to use the `with` statement as Douglas Crockford told me (http://yuiblog.com/blog/2006/04/11/with-statement-considered-harmful/) that bad unforseen things can happen on its usage
sod
2010-09-14 14:18:57
@annakata unfortunatly the pre-edit would only add `{}` to the array if it didn't already exist, and leave it as is otherwise. I realized this shortly after I posted. @Spudley - please explain why its usage is harmful in this case. @sod - and what bad unforeseen things could possibly happen with this simple line of code? There is no ambiguity at all.
MooGoo
2010-09-14 14:25:58
+1 to counter the with-hate: `with` is a powerful tool whether crockford likes it or not, it's just a matter of understanding the tool *as is everything else*. A good coder knows when to break rules.
annakata
2010-09-14 14:33:50
@MooGoo - ah, subtle - I read the OP as wanting exactly that, but you're right it could go either way. Well that's a much more boring question now :)
annakata
2010-09-14 14:35:42
Spudley, sod: a better rule would be to read the articles of influential people carefully and then think about it for yourself before making your mind up. Crockford or anyone else saying that `with` is evil evil evil does not make it true.
Tim Down
2010-09-22 16:01:35
A:
Just a tiny tweak to your idea to make it work
var obj = (obj || []).concat([{}]);
Peter Bailey
2010-09-14 13:59:17
Although, `concat` actually returns a completely new array... Meaning if obj was already defined (which i'm still curious how that might happen), it will not have the `{}` added to it in any parent scope...
gnarf
2010-09-14 14:01:57
That's true, but there's no scope information in the original question. Also, since he's using an assignment statement in his attempt, mutation clearly isn't a requirement.
Peter Bailey
2010-09-14 14:24:15
His original seems to state: `obj` should either stay as it is, or become an empty array, then `push` something onto it... The problem being that `push` wouldn't happen on the original `obj` so if that `obj` was a reference to a different array, or a function parameter, etc... your code would not do the same thing...
gnarf
2010-09-14 16:03:54
The code in the accepted answer refutes the point you're trying to make. `obj.push()` executes no matter what the original state of `obj` is
Peter Bailey
2010-09-14 18:34:39