RJS conditional element replacement

rubyonrails-talk
1

Hi all,

I have an RJS problem. I'm trying to write a helper method that replaces a given div element with a given partial, if and only if that div exists. I can do this with something like:

page << "if($('my_div')){" page[my_partial].replace :partial => 'my_partial' page << "}"

The problem with this (apart from it being ugly code) is that the partial my_partial is rendered even if the div element my_div doesn't exist. In my app, some of the partials I want to use here are pretty complex, and rendering them unnecessarily causes a pretty serious slowdown. Does anyone know of a way to solve this problem?

Many thanks

2

When the client makes the ajax request, it could specify whether or not it has it. Fundamentally the server can't know that sort of stuff unless told.

Fred

3

Thanks Fred, that is a good point! There's a lot of places that I want to do this, so I'd want to automate the process of specifying what elements are present. Perhaps it would be possible to use an Ajax.Responder method to collect a list of divs that are present on the page and send it with each Ajax request? I'm not really sure how to do this, and how to access the JS variables from Rails (as it's the RJS script which I want to prevent from rendering templates). I may be overcomplicating the issue... any thoughts?

4

Thanks Fred, that is a good point! There's a lot of places that I want to do this, so I'd want to automate the process of specifying what elements are present. Perhaps it would be possible to use an Ajax.Responder method to collect a list of divs that are present on the page and send it with each Ajax request? I'm not really sure how to do this, and how to access the JS variables from Rails (as it's the RJS script which I want to prevent from rendering templates). I may be overcomplicating the issue... any thoughts?

The with option to the various remote helpers might be useful, so

link_to_remote 'Foo', :url => {...}, :with => "{foo: foo, bar: bar}" will submit the javascript parameters foo and bar. You can of course
have pretty much any javascript in there. Collecting all the divs on the page would probably be over the top
though, i'd trip it down to link_to_remote 'Foo', :url => {...}, :with => "{needsRefresh: !$ ('foo')}", so needsRefresh will be false if $('foo') exists

Fred

5

Thanks Fred, that worked a treat :slight_smile:

Interestingly, when I used the syntax you suggested ("{needsRefresh: !$ ('foo')}"), the needsRefresh variable wasn't available to the RJS script, at least not in the params hash. Instead I pieced together a string argument of the form "'foo='+$('foo')+'&bar='+$('bar')" and passed this to the :with option. This was then available in the params hash.

Again, thanks for your help!