In case I do:
data-bind="attr: {'id': $index}"
than IDs are 0, 1, 2... but if I do:
data-bind="attr: {'id': $index>0 ? 'choice'+$index : 'choice'}"
than ID is always 'choice', what do I do wrong?
It is Knockout v3.4.2
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Possible duplicate of knockout.js using $index with if binding, stackoverflow.com/questions/11302338/…, stackoverflow.com/questions/17734415/…Jeff Mercado– Jeff Mercado2017-08-23 08:14:25 +00:00Commented Aug 23, 2017 at 8:14
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It is a duplicate, but from my perspective didn't know what to search for, thought the condition syntax could be wrong.skobaljic– skobaljic2017-08-23 08:18:30 +00:00Commented Aug 23, 2017 at 8:18
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1 Answer
$index is actually an observable. In a simple binding, knockout will handle it automatically. In a more complex expression, it doesn't, you need to manually call it:
data-bind="attr: {'id': $index()>0 ? 'choice'+$index() : 'choice'}"
They all end up with just 'choice', because $index>0 will always evaluate to false, since it's comparing the text representation of the $index observable function with 0. This function starts with f and "f" > 0 is false.
3 Comments
skobaljic
Yes, that makes sense and it works. But I have never found docs about 'simple' and 'complex' binding, always had problems with that :(
James Thorpe
@skobaljic Just think of anything other than an observable by itself (as per your first example) as "complex".
skobaljic
I get it, no problems, but never find explanation in docs, was something I had to figure myself. Is there any docs about it? Something that says: If you bind observable only, than you need no brackets?