Execute Javascript function from Rails controller (without rendering or reloading the view)

Question

Is it possible to execute a Javascript function included in application.js or the corresponding js.coffee file from a controller, but without rendering or reloading the view? Ie just a simple

def connect()
  call js: "connect_through_javascript();"
  render :nothing => true
end

but instead of rendering :nothing, is there some way the view could be left untouched? Also would it be possible to send params with it, ie

def connect(param1, param2, param3)
  call js: "connect_through_javascript(#{param1}, #{param2}, #{param3});"
  render :nothing => true
end

The Javascript function called will in turn go to another controller action for it's callback.

I'm about to try with the Paloma gem, but I just wanted to know if any of this is possible without adding dependencies.

Answer 1

What you want is AJAX. JavaScript will then have to do something intelligent with the HTTP response body in the success callback if using a JavaScript library, like jQuery, or if the readyState is 4 and the status is 200 if using native JavaScript.

You're stuck with the HTTP request-response lifecycle.

EDIT: Here is a simple example:

The HTML

<ol id="comments"></ol>

<script type="text/javascript">
    var xhr = new XMLHttpRequest();

    xhr.onreadystatechange = function() {
        if (this.readyState === 4 && this.status === 200) {
            document.getElementById("comments").innerHTML = this.responseText;
        }
    };

    xhr.open("GET", "/posts/123/comments_ajax");

    xhr.send(null);
</script>

The Rails Controller

class PostsController < ApplicationController

    def comments_ajax
        @comments = Comment.where(:post_id => params[:id])
    end

end

The contents of app/views/posts/comments_ajax.html.erb :

<%= @comments.each |comment| do %>
    <li><%= comment.text %></li>
<% end %>