Develop Reference

Rails update element based on AJAX request?

I've been reading a lot about Rails and AJAX and 5.1 Unobtrusive javascript. It explains a lot about responding to Rails version of AJAX calls with a .js file for example.
However what im wanting to do isn't serving up an entire .js file, it's simply updating an element after a <% link_to %> POST request. From my understanding setting remote: true submits it as a AJAX request.
Essentially I have a "Post" which a user can like via a linked Like button. This sends a POST request to the "Post" controller which updates a post to liked and adds a like to the post.
Unfortunately to see the effects of the post being liked (Which is simply that the link changes color as well as the font-awesome icon) you need to refresh the page. I basically want it to update without needing refresh.
I "think" based off what i've read I need to make a respond do and respond via .js to the request with a .js file in the view I want to update (for instance if the controller action is called "like", maybe a like.js.erb file in the view im updating?). But I don't want to serve an entire new page..or would this simply just run the .js?
Then I could do something like $('i.fa-icon#id').style.color = "blue" or something? (Im assuming I can send data from the controller to the .js.erb file?). Not sure the best way to do this, don't rails elements a lot of times have some sort of data-attribute or something (Im still a beginner at this).

Your description is quite correct!
Opposed to the other answer, you don't even need a event listener but as you said you want to have a respond_to in the controller.
So starting from the html:
# post/index.html.erb
<div id="like-button">
<%= button_to "Like this post", post_path(#post), remote: true %>
</div>
Note, that when you use a button_to helper it'll be a POST request by default.
If you click it, it'll go to the controller#update, which you want to change to this:
#posts_controller.rb
...
def update
#post.save
respond_to do |format|
format.html { redirect_to post_path(#post) }
format.js # <-- will render `app/views/posts/update.js.erb`
end
end
Note: the format.html is rendered when JS is disabled.
Now in the scenario that JS is enabled, it executes the app/views/posts/update.js.erb file. It can look like this:
const likeButton = document.getElementById('like-button');
likeButton.innerHTML = '<%= j render "posts/liked-link", post: #post %>';
What is the last line doing? Of course, you can change the style directly with the JavaScript, but you can also render a new partial - and this you will create in a new html file:
# app/views/posts/liked_link.html.erb
<div id="like-button ">
<p>"You liked this post!" </p>
</div>
I just changed the link/button to ap now, but of course you can do whatever you want.
Hope that makes sense :)

Not sure if I understand the question, but if you want to update like button:
What you want to do is to add an event listener to the button, and when clicked it makes a POST request to whatever route handles the likes(with the correct parameters) and your controller should respond with the like object (or whatever in the database gets stored). Have your post request on success method to grab the like button and change it to whatever you want it to look like
$(“#like-btn”).click(function(){
Rails.ajax({
url: "/some/url/to/like/controller",
type: "post",
data: [your post data],
success: function(data) { $(`#${ data[“btn-name”] }`).attr(“color”, “blue”; }
})
}
You can stick this script right in the bottom of the html page
You don’t have to do it exactly like this, just giving you an idea of how to set up the pattern of having JavaScript and Ajax handle the post request and updating of the frontend instead of using html buttons

Respond with *.js.erb using nonce strategy for CSP

I'm implementing a CSP using rails 5.2.1 content security policy DSL. I've got my policy set to something like:
Rails.application.config.content_security_policy do |policy|
policy.default_src :self, :https
policy.connect_src :self
#...
policy.script_src :self
end
# If you are using UJS then enable automatic nonce generation
Rails.application.config.content_security_policy_nonce_generator = -> request { SecureRandom.base64(16) }
I also have <%= csp_meta_tag %> in my application.html.erb
At this point I need to add a nonce: true flag to any inline scripts for these to satisfy the policy. I've done this and it works as expected. However, I'm having trouble maintaining existing AJAX style functionality. For example, I have something like (note the remote: true):
# index.html.erb
<%= link_to create_object_path, id: "#{object.code}",method: :post, remote: true do %>
<button type="button">Create object</button>
<% end %>
In my controller
def create
#object = current_user.object.create
respond_to do |format|
if #object
format.js
else
redirect_back
format.html
end
end
end
In my *.js.erb file
$("#<%= #object.service.id %>").text("Added!");
The object is successfully created but I believe the policy is blocking the above "Added" success message that I add to the DOM. I have not seen any errors in the console so I'm not sure where to go from here.
My understanding in this scenario is script tags are temporarily inserted with the contents of the *.js.erb file and these script tags do not contain the nonce. Or, it is a mismatch.
I've been stuck on how to troubleshoot from here. Any guidance here is much appreciated even if different architectural pattern for sending data to client is the way forward. Thanks in advance.

I ran into a similar issue. In my case, it didn't refuse to run the js.erb file itself but rather scripts in templates nested within that file through the use of render. So, this answer may have limited utility to your specific case. That said, I did try to reproduce your issue using Rails version 6.1.1 and couldn't.
However, even if you get past the initial hurdle of getting just your .js.erb file to run, you can still run into the issue of nested scripts: if your .js.erb file renders a template that contains a script tag. That script won't run because the request from which it originated assigns it a new nonce, which won't match the nonce in the meta tag.
So, to those coming here from a search engine as I did, here's the general strategy I pursue to get async embedded JS working with CSP for that nested case and assuming the .js.erb file itself runs. Using your case as an example:
Send the nonce along in the AJAX request. I suppose you won't get around writing some custom JS to send the request. Something like:
document.getElementById('<%= object.code %>').addEventListener('click', e => {
e.preventDefault(); // So we don't send two requests
fetch('<%= create_object_path %>', {
method: 'POST',
headers: {
'Content-Type': 'application/json;charset=utf-8'
},
body: JSON.stringify({
nonce: document.getElementsByName('csp-nonce')[0].content
})
});
});
This sends the nonce from the meta tag to the server in the form of a nonce parameter.
You may need to remove remote: true from your link for this to work. And of course, this script will itself need to be 'nonced' or else it won't run!
Assign the nonce to a #nonce instance variable in the controller:
#nonce = params[:nonce]
Wherever you render scripts, do:
<%= javascript_tag nonce: #nonce || true do %>
...
For those wondering how to get the same to work with their existing asynchronous forms:
Add this form field: <%= hidden_field_tag :nonce %>
On form submit, assign the nonce from the meta tag to the hidden field:
document.getElementById('id_of_submit_button').addEventListener('click', async e => {
document.getElementById('nonce').value = document.getElementsByName('csp-nonce')[0].content;
});
In this case, you don't want to prevent the default behavior on the event because you want the form to submit.
Then continue with step 2 above (assigning the nonce to a controller instance variable).
I hope as a general strategy this is useful to some. And I hope it can serve as inspiration for how to get the .js.erb file itself to run.
UPDATE: Of course, for your specific (but limited) use case, you could simply return the object's service id as part of some JSON object you return to the client instead of rendering a .js.erb template. I say "limited" because this won't work for people who really need to render templates.
If you did want to render your .js.erb file, I suspect something like this could work for your case as well, where instead of checking whether the HTTP_TURBOLINKS_REFERRER header is present, you check for request.xhr?. Just know that starting in newer Rails versions, remote: true doesn't set the requisite header for request.xhr? to work anymore. But since you're on 5.2.1, it may work for you.

is it possible to set boolean value to a session variable based on some conditions, from javascript?

I'm trying to set a boolean value to session from javascript in rails. my code is as follows
function function_name(e){
if (e.innerHTML == '+') {
<% session[:open] = true %>
}
else {
<% session[:open] = false %>
}}
but i'm getting 'false' value to session[:open] always. conditions are satisfying when I put alert and checked. if this way is not possible, how can I set session value from javascript ?
looking for a solution other than ajax request to controller.

Use cookies if you don't want to make ajax requests. For first time visitors you may want to reload the page if the cookie isn't set.
This topic is nicely covered in this article (the backend is php but it really doesn't matter in this case): https://css-tricks.com/server-side-mustard-cut/

Rails 3 Passing a variable from link_to to javascript

If a user is on a form page, I am trying to throw a confirm message if they navigate away without clicking the update button.
The coffeescript code I am using is as follows
# used to detect if a user is navigating off a page
if form_click == true
window.onbeforeunload = ->
"You have unsaved data! do you really want to exit?"
If I use if 1 ==1 or 1 ==2 as a test case, it works perfectly fine. However, I am having diffculty in sending a variable from the link_to code to set form_click.
I have tried the following
<%= f.button :button, :class => 'btn-primary',
data: {form_click: true},
remote: true %>
But I am not able to pass the variable to the coffeescript code. I am definitely not proficient with javascript and coffeescript, as this probably shows, and would be grateful of any advice on how to resolve this would be much appreciated

Have a look at the generated HTML. I suspect that the link_to is creating something similar to:
<button class="btn-primary" data-form_click="true" data-remote="true"></button>
If so then the coffeescript you need to have would be something like:
$('data-form_click').click( ->
if $(this).attr('data-form_click') == 'true'
window.onbeforeunload = ->
confirm("You have unsaved data! Do you really want to exit?")
)
The code above is off the cuff, but the main point is that the attribute on the button is a string, not a boolean, so you need to adjust accordingly.
Use the JS debugging tools to place a breakpoint so you can inspect the value of form_click is also another way to see what you should be comparing to.

Include a Coffeescript file with ERB in a view

This is giving me a major headache...
So I have an app which requires a sidebar that lists various information to do with a user's player. One section of this sidebar is a friends list. Now, when Player A sends a friend request to Player B, the request should be automatically logged in B's sidebar, and I intend to use WebSockets to do this.
Here is my cp.js.coffe.erb file (there's only a few snippets of ERB at the moment; there will be loads more and I rather get this working first):
$ ->
$("#cp").accordion()
if `"WebSocket" in window`
socket = new WebSocket("ws://localhost:8080")
socket.onopen = =>
console.log("Connection Open")
init = {
sender: "cp"
action: "init"
user: <%= #user.id %>
token: <%= cookies["remember_token"] %>
}
socket.send(init.to_json)
socket.onerror = (e)=>
console.log(e)
socket.onclose = =>
console.log("Closed")
socket.onmessage = (m)=>
console.log("Recieved: #{m.data}")
msg = m.data.JSON.parse
switch msg.action
when "ret_init"
when "friend_udt"
refreshFriend()
refreshFriend() ->
html = "<%= j render 'layouts/friends' %>"
$('#friends').empty()
$('#friends').add(html)
Theoretically, the code itself works fine, the problem being that Rails doesn't let you use ERB in the assets pipeline, and so this file has to sit in app/views/layouts.the file cannot access the variables declared within a controller or use the render method (or most other ERB methods).
Here's the thing: I can't include said file in my application.html.erb file, and I looked into requesting the file with AJAX, but from my understanding that will immediately execute the Javascript once and once only, and I need the methods in this to be constantly available to update the sidebar.
Is there any way of including this file so that it works with the ERB and the CoffeScript so that it would be continuously avaliable to the page? Am I misunderstanding the whole AJAX requesting method?
Thanks #nzifnab for your help with the JS. Now my friends partial looks like this:
<ul id="friendlist">
<% if Relation.find_by(owner: #user.id, type: "freq") != nil %>
<% Relation.find_by(owner: #user.id, type: "freq").each do |r| %>
<li class="friend-request-cp"><%= link_to "/#{User.find(r.character).name}" %></li>
<% end %>
<% end %>
<% if Relation.find_by(owner: #user.id, type: "friend") != nil %>
<% Relation.find_by(owner: #user.id, type: "friend").each do |r| %>
<li class="friend-cp"><%= link_to "/#{User.find(r.character).name}" %></li>
<% end %>
<% end %>
</ul>
I need to apply two different styles to each item, hence why I'm using the ERB here. This works fine, as it's loaded when the page is first navigated to, but my code was supposed to re-render that partial every time a notification comes through of any new interactions. It would then repopulate the list using the data from the database again. Is there a more efficient way of doing this? Can I still do this with the hamlcoffeeassets gem you showed me?
Slight tangent ensues:
By the way, I'm using Ruby 2.0.0-p247 and Rails 4 on Windows 7. I felt the need to include that because of some major compatibility issues with gems that are much different from Ubuntu. I had to move from Ubuntu to Windows because updating from 13.04 to 13.10 broke everything Ruby Gem on that OS. I don't have tome to find a fix: I literally have only four days to get this app built.

You can kinda use erb in the asset pipeline, but you have to remember that it only gets rendered ONCE, EVER, and not once for every user and so even if there was an #user variable (which there won't be), it would never change. You can use erb in your coffee file for things like route paths and environment variables, but not for things like user-specific config and dynamic changes to the JS. It's bad practice anyway.
What you should really do is use a javascript library to read cookies instead of trying to do it with rails (This will give you access to some of the things you appear to be trying to do). And when you need more dynamic behavior you should render data-attributes or other values into the html DOM itself and use the javascript to read that.
Take a look at this cookie library: https://github.com/carhartl/jquery-cookie
There's many others to look at via a quick google search.
socket.onopen = =>
console.log("Connection Open")
init = {
sender: "cp"
action: "init"
user: $.cookie('user_id')
token: $.cookie('remember_token')
}
There are a couple of ways to render new markup for your view using JS. One way is to use js templates. I'm a big fan of the hamlcoffeeassets library here: https://github.com/netzpirat/haml_coffee_assets Although it uses haml for the view, and not ERB. There are ERB variants as well.
You would add some markup to app/assets/templates/friend.jst.hamlc like so:
%p This is my friend markup #{#friend.name}
And then you can render it from your JS like this:
$('#friends').append(JST['templates/friend'](friend: {name: 'Bob'}))
Which will append the markup from your template with the values you've passed interpolated in. In my example you'd end up with this markup inside your #friends container:
<p>This is my friend markup Bob</p>
Alternatively you can render the partial you want via rails into your JSON response as just a string, and then insert that into your document...
So your JS might look something like this:
socket.onmessage = (m)=>
console.log("Recieved: #{m.data}")
msg = m.data.JSON.parse
switch msg.action
when "ret_init"
when "friend_udt"
refreshFriend(msg.friendHTML)
refreshFriend(html) ->
$('#friends').html(html)
UPDATE
In reference to your ERB question... First of all your partial is incredibly inefficient making similar calls to the database four times every time you render it. haml_coffee_assets is for use with the haml markup language (which I prefer over ERB), if you want ERB then use eco instead: https://github.com/sstephenson/eco
If you want to render this in the JS, then you need to send this "friend relation" data as JSON through the notification data response, you do not have access to active record OR any controller methods or instance variables when rendering javascript partials - they don't hit back to the server, they only use what is accessible by your javascript at the time.

This should really go to app/assets/javascripts/cp.js.coffee.erb, you can use erb in the asset pipeline just fine (see here) Make sure you are spelling the coffee extension right, though!
Doing this, you should be able to call this via ajax without problems, the path would be /assets/cp.js.

try this gem: 'coffeebeans'
name your coffee file as "some_file.html.erb"
<%= coffeescript_tag_do %>
# your coffee script here ...
<% end %>
in another erb file:
<%= render file: '.../some_file' %>