File: README — Documentation for render

render_async

Speed up rendering Rails pages with this gem.

render_async renders partials to your views asynchronously. This is done through adding JavaScript code that does AJAX request to your controller which then renders your partial into a Rails view.

Workflow:

user visits a Rails page
AJAX request on the controller action
controller renders a partial
partials renders in the place where you put render_async helper

JavaScript is injected into <%= content_for :render_async %> so you choose where to put it.

Installation

S Add this line to your application's Gemfile:

gem 'Sender_async'

And then execute:

$ bundle install

Usage

Include render_async view helper somewhere in your views (e.g. app/views/comments/show.html.erb):
```
<%= render_async comment_stats_path %>
```

Then create a route that will config/routes.rb:

get :comment_stats, :controller => :comments

Fill in the logic in your controller (e.g. app/controllers/comments_controller.rb):

def comment_stats
  @stats = Comment.get_stats

  render :partial => "comment_stats"
end

Create a partial that will render (e.g. app/views/comments/_comment_stats.html.erb):
```
<div class="col-md-6">
  <%= @stats %>
</div>
```
Add content_for in your base view file in the body part (e.g. app/views/layouts/application.html.erb):
```
<%= content_for :render_async %>
```

Advanced usage

Advanced usage includes information on different options, such as:

Passing in HTML options
Passing in an HTML element name
Passing in a placeholder
Passing in an event name
Caching
Using with Turbolinks
Using with respond_to and JS format
Nested Async Renders

Passing in HTML options

render_async takes two arguments, path and html_options.

path is the AJAX-capable controller action you're looking to call via GET. e.g. comments_stats_path, posts_path, etc.
html_options is an optional hash that gets passed to a rails javascript_tag, to drop html tags into the script element.

Example of utilizing html_options with a nonce:

<%= render_async users_path, nonce: 'lWaaV6eYicpt+oyOfcShYINsz0b70iR+Q1mohZqNaag=' %>

Rendered code in the view:

<div id="render_async_18b8a6cd161499117471">
</div>

<script nonce="lWaaV6eYicpt+oyOfcShYINsz0b70iR+Q1mohZqNaag=">
//<![CDATA[
  ...
//]]>
</script>

Passing in an HTML element name

render_async can take in an HTML element name, allowing you to control what type of container gets rendered. This can be useful when you're using render_async inside a table and you need it to render a tr element before your request gets loaded, so your content doesn't get pushed out of the table.

Example of using HTML element name:

<%= render_async users_path, html_element_name: 'tr' %>

Rendered code in the view:

<tr id="render_async_04229e7abe1507987376">
</tr>
...

Passing in a placeholder

render_async can be called with a block that will act as a placeholder before your AJAX call finishes.

Example of passing in a block:

<%= render_async users_path do %>
  <h1>Users are loading...</h1>
<% end %>

Rendered code in the view:

<div id="render_async_14d7ac165d1505993721">
  <h1>Users are loading...</h1>
</div>

<script>
//<![CDATA[
  ...
//]]>
</script>

After AJAX is finished, placeholder will be replaced with the request's response.

Passing in an event name

render_async can receive :event_name option which will emit JavaScript event after it's done with fetching and rendering request content to HTML.

This can be useful to have if you want to add some JavaScript functionality after your partial is loaded through render_async.

Example of passing it to render_async:

<%= render_async users_path, :event_name => "users-loaded" %>

Rendered code in view:

<div id="render_async_04229e7abe1507987376">
</div>

<script>
//<![CDATA[
  ...
    document.dispatchEvent(new Event("users-loaded"));
  ...
//]]>
</script>

Then, in your JS, you could do something like this:

document.addEventListener("users-loaded", function() {
  console.log("Users have loaded!");
});

Caching

render_async can utilize view fragment caching to avoid extra AJAX calls.

In your views (e.g. app/views/comments/show.html.erb):

# note 'render_async_cache' instead of standard 'render_async'
<%= render_async_cache comment_stats_path %>

Then, in the partial (e.g. app/views/comments/_comment_stats.html.erb):

<% cache render_async_cache_key(request.path), :skip_digest => true do %>
  <div class="col-md-6">
    <%= @stats %>
  </div>
<% end %>

The first time the page renders, it will make the AJAX call.
Any other times (until the cache expires), it will render from cache instantly, without making the AJAX call.
You can expire cache simply by passing :expires_in in your view where you cache the partial

Using with Turbolinks

On Turbolinks applications, you may experience caching issues when navigating away from, and then back to, a page with a render_async call on it. This will likely show up as an empty div.

To resolve, tell turbolinks to reload your render_async call as follows:

<%= render_async events_path, 'data-turbolinks-track': 'reload' %>

Make sure to put <%= content_for :render_async %> in your base view file in the <head> and not the <body>.

Using with respond_to and JS format

If you need to restrict the action to only respond to AJAX requests, you'll likely wrap it inside respond_to/format.js blocks like this:

def comment_stats
  respond_to do |format|
    format.js do
      @stats = Comment.get_stats

      render :partial => "comment_stats"
    end
  end
end

When you do this, Rails will sometime set the response's Content-Type header to text/javascript. This causes the partial not to be rendered in the HTML. This usually happens when there's browser caching.

You can get around it by specifying the content type to text/html in the render call:

render :partial => "comment_stats", :content_type => 'text/html'

Nested Async Renders

It is possible to nest async templates within other async templates. When doing so, another content_for is required to ensure the JavaScript needed to load nested templates is included.

For example:

<%# app/views/comments/show.html.erb %>

<%= render_async comment_stats_path %>

<%# app/views/comments/_comment_stats.html.erb %>

<div class="col-md-6">
  <%= @stats %>
</div>

<div class="col-md-6">
  <%= render_async comment_advanced_stats_path %>
</div>

<%= content_for :render_async %>

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.