Rails%203%20In%20Action

Using JavaScript
What does matter here is the number variable that identifies the number of file
fields you are currently up to. You specify the child_index option in your fields_for
so that each time these fields are rendered, they’re given different identifiers. The
assets form partial gets this number variable only from the tickets partial; you’ve yet to
set up a way the new action sets this variable. Without this variable set in the new
action, you can’t render the app/views/files/_form.html.erb for a new asset without
knowing what number you’re up to. Let’s set that up now.
9.4.5 Sending parameters for an asynchronous request
The number variable indicates what file field you are up to, so you need a way to tell
the new action in FilesController how many file fields are currently on the page.
Previous versions of Rails had an option for this called :with, which has now, unfortunately,
been removed. No matter, you can do it in JavaScript. It’s better to put this
code in JavaScript anyway, because it’ll already be using some to determine the number
to pass through. Rather than using pure JavaScript, you’ll be using CoffeeScript,
which comes with Rails 3.1 but can be used in any other language. Let’s learn some
CoffeeScript now.
LEARNING COFFEESCRIPT
CoffeeScript is, in the words of its website, “a little language that compiles into
JavaScript.” It’s written in a simple syntax, like this:
square = (x) -> x * x
This code compiles into the following JavaScript code:
var square;
square = function(x) {
return x * x;
};
In the CoffeeScript version, you define a variable called square. Because this isn’t yet
initialized, it is set up using var square; in the JavaScript output. You assign a function
to this variable, specifying the arguments using parentheses (x) and then specifying
the code of the function after ->. The code inside the function in this case is
converted into literal JavaScript, making this function take an argument, multiply it by
itself, and return the result.
Although this is a pretty basic example of CoffeeScript, it shows off its power. What
you would write on four lines of JavaScript requires just one line of extremely easy-tounderstand
CoffeeScript.
Each time you generate a controller using Rails, a new file called app/assets/
javascripts/[controller_name].js.coffee is created. 8 This file is created so you have a
location to put CoffeeScript code that is specific to views for the relevant controller.
This is really helpful in your situation, because you’re going to use some CoffeeScript
to tell your Add Another File link what to do when it’s clicked.
8 If you have the coffee-rails gem in your Gemfile.
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