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Pass array from JavaScript to Ejs

Is there any way we can pass values from javaScript to ejs without using document.createElement?
My View Engine is set as 'ejs' in express. I am making single page application and fetching data via vanilla JS. Upon request server is responding with array:
array = [{name:'anthony', age:'20'}, {name:'John', age:'25'}]
Now, I want to loop through this array and render the values in DOM without using document.createElement.
I cannot render the page directly from server as res.render('index',{array}) and do something like:
<% array.forEach(data => {%>
<h3><%= data.name %></h3>
<%= data.age %>
<% })%>
I am sending data as res.json({array}) and the data needs to be rendered from client side Vanilla Javascript.

javascript function with activerecord input

I have a Ruby on Rails app. After users/home is rendered, it sends an ajax call to users#feed. The action feed performs a query and sends a list of users to feed.js.erb in which I can mix javascript and erb to render the users on the page. However, to make the code neat, I'd like to create a javascript function that takes the database object (list of users) as input and renders them on the page. This way I can use this function in other pages, too. What is the best way to do that? Is it possible to convert the activerecord database object to some javascript object that I can easily work with (do things similar to users[0].name, users[2].address, etc)? One way would be to convert to json or string, but I can get the information (such as users[0].name) easily out of the string.
Here is part of the code in feed.js.erb:
function showUsers() {
<% if #users.empty? %>
alert("no change");
<% else %>
<% #users.each do |user| %>
$("#<%= j user.id %>").html("<%= j user.name %>");
<% end %>
<% end %>
}
showUsers();
Thanks.

You can call JSON.parse() upon #users.to_json
ex: showUsers(JSON.parse(<%= #users.to_json %>))
But you can also return the information as json, instead of js.erb. So you would have this function on the client side and would pass the users object to your function on the AJAX callback.

Passing javascript variable into erb tag

I've been looking into how to use a javascript variable within erb <% %> tags. This will have to be done via AJAX (see How to pass a javascript variable into a erb code in a js view?). I'm quite new to JS and especially new to AJAX and finding an example of this in action would be awesome.
Consider the following simple scenario where all that is needed to be passed from the JS to the ERB is a simple bit of text:
HTML:
<input id="example-input" type="text">
$(function() {
$('input#example-input').keyup(function(e) {
if(e.keyCode == 13){
var input = $('input#example-input').val();
<% puts input.upcase %>
}
}
});
Notice that the input will not be defined within the erb tags, and hence this will throw an error.

I believe you're assuming that the line <% puts input.upcase %> will execute ruby code after your javascript line var input = $('input#example-input').val();. If that is what you were thinking, this is incorrect. In the example you've given:
The <% puts input.upcase %> gets executed when the page loads.
input in <% puts input.upcase %> is a ruby variable
input in var input = $('input#example-input').val(); is a javascript variable
If you had a variable that you set on the server side, you could say something like this in your javascript:
var my_js_var = '<%= a_str_in_ruby %>';
and that would work fine for intializing a variable on the javascript side.
However since you want to request data from the client side (aka javascript) to your server side (to be handled by rails controller), what you should be doing is submitting an ajax request. There's a section in the rails documentation that contains examples, and a good railscasts episode (if you're a paying member).

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' %>

Rails 3.2 js.erb file escaping JS

I am new to rails and I am confused by something.
I am using a js.erb file to show me a list of products fetched from the server. What I am confused at is how I can do this in js.erb file and it works:
<ul class="list-bordered" id="products">
<%= render_cell :businesses, :index, {:businesses => #businesses} %>
</ul>
<%= render :partial => 'partials/infinite', :locals => {:segment => businesses_path, :container => '#businesses'} %>
and every other JS code is escaped, thus
var t = 0;
is output in the page as "var t=0;"
I checked the server logs and the response is indeed JS. I am using respond_with, and checked that I am indeed responding to JS requests.
SIDE QUESTION: Speaking in a "best practice way", is it alright to have html code inside a .js.erb file?
Thanks in advance!

Since you are firing an AJAX request, it's data type is script now and in a .js.erb file you can write Javascript code easily .
$("#products").html("<%=escape_javascript(render_cell :businesses, :index, {:businesses => #businesses}%>")
Now you can manipulate your .js.erb or HTML as per your wish; it's just an example how can you render a partial in a .js.erb.
Now suppose you are rendering HTML on the client side (considering data type is text/html). On an AJAX success, you have to replace that HTML.