Posting from javascript to ruby

Question

So I have this chunk of code on the view:

var variable_test = 'begin';
$.ajax({
  url : "/controller/index",
  type : "post",
  data : variable_test
}).done(function(response) {
  alert('1');
})
    .fail(function (error) {
    alert('2');
});

var eia = <%= @variable.to_json.html_safe %>;
alert(eia);

and on controller I have this:

def index
   @someVariable = 'end'
   @variable = params[:variable_test]
end

on execution this would be the result:

dialog message with 1 (so it was supposed to have worked and posted something)

dialog message with null

and this is the server side POST request:

Started POST ...  
Processing by Controller#index as */*  
Parameters: {"begin"=>nil}  
...  
...  
Current user: anonymous  
...  
Completed 200 OK...

So what is wrong? Is it actually posting the variable variable_test to controller variable ? If yes, why does it reads it as null? How to fix this?

nbermudezs · Accepted Answer · 2015-10-18 01:16:36Z

2

It is sending your value in the post. The problem is that data takes an object as value, so if you want to read the value in the server side as params[: variable_test] you need to make the ajax call

var variable_test = 'begin';
$.ajax({
  url : "/controller/index",
  type : "post",
  data : { variable_test: variable_test },
}).done(function(response) {
  alert('1');
}).fail(function (error) {
  alert('2');
});

On another hand, I'm not sure what you are trying to accomplish, The index action as you have it will try to render the index.html.erb file you have under app/views/controller/, is that the same index action that is being called in the ajax request?

Sorry for not commenting, not enough reputation.

answered Oct 18, 2015 at 1:16

nbermudezs

2,8541 gold badge22 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Pfeiffer Over a year ago

I just want to send info back to server as needed. The way you edited it is still returning null. (and don't mind about not having reputation for comment. I know that situation well.)

Pfeiffer Over a year ago

after updating data on server I would like to read the new value from client.

nbermudezs Over a year ago

When are you getting the alert with null? When you load the page?

nbermudezs Over a year ago

I just created an empty app and added some similar code. Check this

nbermudezs Over a year ago

If you are getting the null when you load the page that is because it is expecting the variable_test argument to be in the url, something like localhost:3000/?variable_test=ilikepotatoes.

|

Richard Peck · Accepted Answer · 2015-10-18 10:12:50Z

1

The way this works is actually quite simple.

Your Ajax seems to be sending your request to your controller:

Started POST ...
Processing by Controller#index as */*
Parameters: {"begin"=>nil}

... it's your response which is not being caught...

#app/assets/javascripts/application.js
$.ajax({
  url : "/controller/index",
  type : "post",
  data : {serialized: "data"}, // data should be serialized
}).done(function(response) {
  alert('1');
}).fail(function (error) {
    alert('2');
});

This setup should trigger the alert('1') function.

Handling the response is where you're falling short:

1. ERB doesn't work in the asset pipeline

#app/assets/javascripts/application.js
var eia = <%= @variable.to_json.html_safe %>; // won't work
alert(eia); // won't work

This will not work.

What will is to use the returned data inside the ajax .done method:

#app/controllers/controller_controller.rb
class ControllerController < ApplicationController
   def index
      @variable = {}
      @variable.attribute = "test"
      respond_to do |format|
         format.json { render json: @variable }
      end
   end
end

#app/assets/javascripts/application.js
$.ajax({
  url : "/controller/index",
  type : "post",
  data : {serialized: "data"}, // data should be serialized
}).done(function(response) {
   json = JSON.parse(response);  
   alert(json.attribute)
}).fail(function (error) {
    alert('2');
});

This should return the data, allowing you to output it into the view

--

2. Use Server-Side JS

In addition to the fact that ERB won't work in the front-end, you'll have to look at how your JS is being called.

You must remember that JS is front-end; it doesn't have any access to your Ruby variables. Thus, if you're trying to access the returned data in your view, you either need to capture the response from the server (#1), or run server-side JS like this:

#app/controllers/controller_controller.rb
class ControllerController < ApplicationController
   def index
      respond_to do |format| 
         format.js #-> calls app/views/controller/index.js.erb
      end 
   end
end

This will invoke index.js.erb whenever you run the index action - allowing you use any of the data you've defined in Ruby:

#app/views/controller/index.js.erb
var eia = <%= @variable.to_json.html_safe %>;
alert(eia);

This would also have to coincide with removing the response hooks in your front-end ajax:

#app/assets/javascripts/application.js
$.ajax({
  url : "/controller/index",
  type : "post",
  data : {serialized: "data"}, // data should be serialized
});

answered Oct 18, 2015 at 10:12

Richard Peck

76.8k9 gold badges98 silver badges148 bronze badges

3 Comments

Pfeiffer Over a year ago

I don't get it yet. 'var something = <%= ATserverVariable %>' Isn't supposed to be processed on server side so it will return a page with that variable value when it was requested? So lets say I post something to 'serverVariable', if someone else request it again, its not supposed to get a new value? I want to update datas on server in a way that the client side can request the new value. Also, you said that 1 - var eia = <%= ATvariable.to_json.html_safe %>; won't work, but that line of code is recovering the proper value of the variable, so why did you say it won't work?

nbermudezs Over a year ago

So, what you want is a value to be persisted so future visits see that new value? You will need to start using a database for that, the variables in a controller are not persisted. Also, that line of code works because you have in a view, if you had it .js file in your assets pipeline it won't work (note that he named the file to contain that code app/assets/javascripts/application.js. That's what Rich Peck meant.

Richard Peck Over a year ago

JS = client side, Ruby = server side. I can't read Chinese, client-side can't read server-side variables. Two different things; your @variable is a ruby variable, set in the server. That memory is only available to server memory; you cannot load it into JS without "translating" it in ways such as how I've described

Collectives™ on Stack Overflow

Posting from javascript to ruby

2 Answers 2

6 Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related