js.erb is a bad way to learn.
Ruby on Rails can be used as a kind of poor mans Single Page Architecture by using remote: true and returning JS.erb responses. But all it really does it gives you enough rope to hang yourself.
Its a really bad way to learn ajax as it leads to poor code organisation and a very non RESTful application as it leads to a focus on procedures instead of resources.
I instead encourage you to try to learn ajax without mixing ERB and JS. Mixing server side and client side logic just makes everything much more complicated as you have to keep track of what is happening where.
Instead you might want to focus on setting up reusable javascript functions in app/assets/javascripts and fetching JSON data instead of javascript procedures.
This will teach you not only to do ajax in Rails but also how to do it with external API's and teach you valuable lessons about how to structure and organise code.
So lets start looking at how to refactor:
Highscores should be a resource.
Lets start by setting up the routes:
resources :highscores, only: [:create, :index, :show]
And the controller:
class HighscoresController < ApplicationController
respond_to :json, :html
def create
@highscore = Highscore.create(highscore_params)
respond_with @highscore
end
def index
@highscores = Highscore.order(score: :desc).all
respond_with @highscores
end
def show
@highscore = Highscore.find(params[:id])
respond_with @highscore
end
private
def highscore_params
params.require(:highscore).permit(:username, :time, :score)
end
end
Responders is a pretty awesome tool that makes it so that we don't have to do a bunch of boilerplate code when it comes to returning responses. Our create method will return 200 OK if it was successful and 422 BAD ENTITY or some other "bad" response code if it failed.
Some javascript scaffolding
Lets set up a little bit of scaffolding so that we can hook our javascript up to a specific controller and action without using inline script tags.
Open up layouts/application.html.erb and replace the <body> tag:
<%= content_tag :body, data: { action: action_name, controller: controller_name } do %>
<%= yield %>
<% end %>
Then add this little piece to applicaiton.js:
// Triggers events based on the current controller and action.
// Example:
// given the controller UsersController and the action index
// users:loaded
// users.index:loaded
$(document).on('page:change', function(){
var data = $('body').data();
$(this).trigger(data.controller + ":loaded")
.trigger(data.controller + "." + data.action + ":loaded");
});
Where is that ajax y'all was talkin' bout?
Lets say we have a list of highscores that we want to update either at regular intervals (polling) or when the user submits a highscore.
// app/assets/javascripts/highscores.js
function getHighscores(){
var $self = $('.highscores-list');
return $.getJSON('/highscores').done(function(highscores){
var elements = $.map(highscores, function(h){
return $('<li>').text([h.username, h.score].join(', '));
});
$self.empty().append(elements);
});
};
$(document).on('games:loaded highscores:loaded', function(){
// refresh highscores every 5 seconds
(function refresh(){
getHighscores().done(function(){
window.setTimeout(refresh, 5000);
});
}());
});
That last part is a bit hairy - its a recursive function that sets a new timer when the ajax call has completed. The reason we use this and not setInterval is that setInterval does not care if the previous call was completed or not.
Creating Highscores.
First lets russle up a form:
<%# app/views/highscores/_form.html.erb %>
<%= form_for(local_assigns[:highscore] || Highscore.new), class: 'highscore-form' do |f| %>
<div class="field">
<%= f.label :username %>
<%= f.text_field :username %>
</div>
<%= f.hidden_field :score %>
<%= f.hidden_field :time %>
<%= f.submit %>
<% end %>
And then lets spiff it up with some ajax goodness:
$(document).on('games:loaded highscores:loaded', function(){
$('#new_highscore').submit(function(e){
$.ajax(this.action, {
data: {
highscore: {
username: this.elements["highscore[username]"].value,
time: this.elements["highscore[time]"].value,
score: this.elements["highscore[score]"].value
}
},
method: 'POST',
dataType: 'JSON'
}).done(function(data, status, jqXHR){
getHighscores();
// todo notify user
});
return false; // prevent form from being submitted normally
});
});
