Bug in Rails’ observe_field and prototype.js
I tried using Rails’ observe_field yesterday, and it didn’t work if you specified the :frequency option with the value set to less than or equal to 0.
Code snippet:
<%= observe_field :item_id,
:frequency => 0,
:update => “this_part”,
:url => {:action => ‘new’},
:with => “‘item_id=’ + value” %>
You would have got a javascript error in prototype.js at
onElementEvent: function() {
var value = this.getValue();
if (this.lastValue != value) {
this.callback(this.element, value);
this.lastValue = value;
}
}
It would seems that nothing was happening if you weren’t on the look out for javascript errors. No big issue. Just remove the :frequency option and you are good to go. The frequency option works fine for values greater than 0.
My version of Rails: 1.2.2
Juice Bar 
Some people will say that it’s not a bug. If :frequency is 0, then it doesn’t make sense to include it, so leave it out.
I classify it as a bug because the book and the document says that you can set :frequency to 0 or less if you want actions taken immediately for an event on the observed field.
I set it to 0, it doesn’t work as it said it should. So it’s a bug.
If I missed anything, or if anyone knows how to make :frequency work with 0 or less, please correct me!