I want to use the variables and functions of rails in javascript using erb.

If you want to pass the value from Rails to javascript, you can write it in the view file as follows.

<%=javascript_tag do%>
    window.hoge='<%=j@hoge%>';
    window.fuga='<%=j params[:fuga]||"Default value"%>;;

    alert(hoge);
    alert(fuga);
<%end%>

You can also use a gem called gon.

Reference Site
http://ja.asciicasts.com/episodes/324-passing-data-to-javascript
http://qiita.com/mosa_siru/items/e69eee47a183b13cfb62
http://qiita.com/yk-212/items/8d648b83e24a43af17ba

I don't have any.

erb only processes eRuby scripts and
AssetPipeline is for compression through compilation, binding, etc.
The GET query (params variable) does not change the code in the output.
http://railsdoc.com/asset_pipeline
(if it is done.What happens to pre-compiled ones?)

If such action is required,
For those views, I prepared the original .js.erb and
It can be implemented by calling a query string from a script tag.