ruby vs js string concatenation in rails

so in my show.html.erb file for onf the controllers i have had

<% content_for :head do %>
<script type="text/javascript"> 
var filepath= "/flexpaper/" + <%=  @exam.filename.to_s %> + ".swf"

        var flashvars = { 
              SwfFile : escape(filepath), ....

now this seemed to be the workaround solution I used but when I tried to achieve the same result the other way around as follows

<% content_for :head do %>
    <script type="text/javascript"> 
    var filepath= &l开发者_C百科t;%= "/flexpaper/" +  @exam.filename + ".swf".to_s  %>

            var flashvars = { 
                  SwfFile : escape(filepath), ....

i.e to generate filepath in ruby rather than javascript I get undefined error for filepath. now i understand that is because of escape as it didn't get filepath as a string i.r "stuff.." rather something like stuff.. so the escape errors out. but I don't see why? any ideas?

P.s- also any suggestions for UJS style organisation. I have every other js residing somewhere in other file and included in header as needed except for this somewhat dynamic one. I can't have ruby code in included js files and didn't wanted to have a javascript controller as like ryan bates railscast to generate this minor script. So any other simple solution.

Essentially, you're missing quotes in your javascript in the second version. After the ruby has run, the generated page contains a script tag with pure javascript. That javascript looks like this:

var filepath= /flexpaper/some_exam.swf
    var flashvars = { 
      SwfFile : escape(filepath), ....

Note that you're assigning a value to the filepath variable, but that it's not surrounded by quotes. It's not valid javascript. If you fix it like this, it should work:

<% content_for :head do %>
  <script type="text/javascript"> 
    var filepath= "<%= "/flexpaper/" +  @exam.filename + ".swf".to_s  %>";
    var flashvars = { 
       SwfFile : escape(filepath), ....

While I was at it, I added a semicolon and fixed your indenting -- you'll find that properly indenting your javascript code makes it orders of magnitude easier to debug. That ruby code will produce javascript that looks about like this:

  <script type="text/javascript"> 
    var filepath= "/flexpaper/some_exam.swf";
    var flashvars = { 
       SwfFile : escape(filepath), ....

A trick to spot errors like this is to do a view-source in your browser, and look carefully at the javascript that's being produced.

I see a couple of errors from your code, in bothe solutions you are missing the quotes that will make some text a string. In the first one you could do like this:

<% content_for :head do %>
  <script type="text/javascript"> 
    var filepath= "/flexpaper/<%=  @exam.filename.to_s %>.swf"

    var flashvars = { 
          SwfFile : escape(filepath), ....

And in the second one you are missing the quotes for the whole string

<% content_for :head do %>
  <script type="text/javascript"> 
    var filepath= "<%= "/flexpaper/" +  @exam.filename + ".swf".to_s  %>"

        var flashvars = { 
              SwfFile : escape(filepath), ....