Use PhantomJS to pre compile handlebars template - ruby-on-rails-4

Question

I have a rails application as back end and a BackboneJS application as front end. BackboneJS app starts with rails server. Now, I have a problem of search engine indexing pages of my application, which I tried to solve with phantomjs [I user this gem]. I wrote a before_filter in application controller like this:
def phantom_response
if params["_escaped_fragment_"].present?
url = "#{request.base_url}/#!#{params["_escaped_fragment_"]}"
output = Phantomjs.run('/lib/assets/get_page.js', url)
render :text => output
end
end
And my get_page.js looks like this:
var page = require('webpage').create();
page.settings.userAgent = 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36';
page.settings.localToRemoteUrlAccessEnabled = true;
page.open(phantom.args[0], function (d) {
var body = page.evaluate(function(s) {
return document.querySelector(s).innerText;
}, '#provider_details_tpl');
console.log(body);
phantom.exit();
});
The element with "provider_details_tpl" contains a handlebars template.
But phantomjs returns just my template without precompilation. Can you help me?