Observe_field in rails 3

I had a dropdown. I need to add a textbox when the value changes in the dropdown.开发者_Go百科 I had done this using "obseve_field" tag in rails 2.3.5. Now I am moving into rails 3. So how I write it in rails 3.

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If you want to use the legacy Prototype helpers (like observe_field) in Rails 3, check out the GitHub repository for prototype_legacy_helper.

Otherwise, you can write this JavaScript yourself using the new UJS. See these two blocks of code for the old observe_field method:

• http://github.com/rails/prototype_legacy_helper/blob/c91b90/lib/prototype_helper.rb#L359-365
• http://github.com/rails/prototype_legacy_helper/blob/c91b90/lib/prototype_helper.rb#L415-429

and see Part 2 at http://www.simonecarletti.com/blog/2010/06/unobtrusive-javascript-in-rails-3/ to see how to do this in jQuery.