How do I modify a global variable in my Rails script from JavaScript?

问题

I have the following variable defined in my Rails controller:

$PATH

In JavaScript I would like to change the value of this variable:

<script>
   $("#resetDefaults").click(function(){
       $PATH = '3'; //try 1
       <%= $PATH %> = '3'; // try 2
   });
</script>

I have tried both of the above statements and can't figure out how to do it.

回答1:

A global variable is only global in the Ruby code that is executed on the server.

You're running JavaScript code in the browser. That code has no direct access to variables on the server.

If you wish to change some state (variable) on the server, you need to call a Rails controller method from your JavaScript code. I.e., you need to do an AJAX call to the server from the browser. Something like this:

$("#resetDefaults").click(function() {
   $.ajax({ url: "<%= url_for(:action => 'update_path_var') %>" });
   return false;
});

Then in the controller you have something like:

def update_path_var
  $PATH = 1234
  render :nothing => true
end

http://api.jquery.com/jQuery.ajax/
http://apidock.com/rails/ActionController/Base/url_for

BTW, in general using global variables in Ruby is not considered good coding practice, unless there is some very specific reason for it.

回答2:

There is no way to achieve that. I think you should do some introduction to web programming course.

来源：https://stackoverflow.com/questions/17196173/how-do-i-modify-a-global-variable-in-my-rails-script-from-javascript