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How to examine the contents of data returned from an ajax call

I have an ajax call to a PHP module which returns some HTML. I want to examine this HTML and extract the data from some custom attributes before considering whether to upload the HTML into the DOM.
I can see the data from the network activity as well as via console.log. I want to extract the values for the data-pk attribute and test them before deciding whether to upload the HTML or just bypass it.
$.ajax({
url: "./modules/get_recent.php",
method: "POST",
data: {chat_id:chat_id, chat_name:chat_name, host_id:host_id, host_name:host_name}, // received as a $_POST array
success: function(data)
{
console.log(data);
},
})
and some of the console log data are:
class="the_pks" data-pk="11"
class="the_pks" data-pk="10"
etc.
In the above data I want to extract and 'have a look at' the numbers 11 and 10.
I just do not know how to extract these data-pk values from the returned data from the ajax call. Doing an each on class 'the_pks' does not work as at the time I am looking at the data they have not been loaded into the DOM.
I have searched SO for this but have not come up with an answer.
Any advice will be most appreciated.

I hope I understand your question.
If you get a HTML as a response, you can always create an element and insert that html inside it, without adding it to the DOM. And after that you can search it as you do with a DOM element.
const node = document.createElement("div");
//then you can do
node.appendChild(data);
// or
node.innerHTML = data;
And after that you can search inside the node:
node.querySelectorAll("[data-pk]")

I will re-engineer this - it was probably a clumsy way to try and achieve what I wanted anyway. Thanks to those who tried to help.

Rails Live: Dynamically send resut from method to browser

I am trying to notify the browser of the user of a change of the status of the model. I am trying to use the live-module of Rails for that. Here is what I have got so far:
require 'json'
class Admin::NotificationsController < ActionController::Base
include ActionController::Live
def index
puts "sending message"
videos = Video.all
response.headers['Content-Type'] = 'text/event-stream'
begin
if(params[:id].present?)
response.stream.write(sse({id: params[:id]},{event: "video_encoded"}))
end
rescue IOError
ensure
response.stream.close
end
end
private
def sse(object, options = {})
(options.map{|k,v| "#{k}: #{v}" } << "data: #{JSON.dump object}").join("\n") + "\n\n"
end
end
The idea behind the above controller is, that when its url gets called with a parameter, it would send this parameter (in this case the id) to the user. Here is how I am trying to call the controller:
notifications_path(id: video.id)
Unfortunately though, the following event-listener in the browser does not fire, even if I use curl to provoke an event:
var source = new EventSource('/notifications');
source.addEventListener("video_encoded", function(event) {
console.log("message")
console.log(event)
});
The goal of this is, that I want to add an dom-element to a certain page (later on) if there is a change. There may be a better way, but Ruby Live seemed like a suitable solution. Any tips or proposals of a different approach are appreciated.

Your use case does not seem like a valid use case for ActionController::Live. You are not sending a streaming output to the browser. You do a one time check on ID and send the JSON output.
Use a regular controller and get the request by AJAX instead of EventSource.

Incorrect JSON data format

I am trying to create some JSON to be used for displaying a chart using Highcharts
http://www.highcharts.com/
I have copied one of their examples:
http://www.highcharts.com/stock/demo/basic-line
Click "View Options" under the graph to see the source. There is also a JSFiddle there to play with
If I copy that locally it all works fine.
The problem is when I try to use my own data source.
I have an ASP.Net MVC controler which is spitting out a list of arrays, just like their data source. However, that doesn't work.
Their datasource looks like this
http://www.highcharts.com/samples/data/jsonp.php?filename=aapl-c.json&callback=?
and they retrieve it like this
$.getJSON('http://www.highcharts.com/samples/data/jsonp.php?filename=aapl-c.json&callback=?', function (data) {
So I thought I'd take a step back and copy thier data exactly and put it in a text file on my server and try that:
So I tried this
$.getJSON('/data.txt', function (data) {
and this
$.get('/data.txt', function (data) {
but neither work
I have also tried using both JSON.parse and jQuery.parseJSON after retrieving the data, but again - that doesn't seem to work
I am also wondering what the ? is at the start of their data
Their data looks like this
?([[<some data>],[some data]]);
I don't get any error message, the graph just doesn't display
any ideas?
SOLVED IT
Just need to retrive the data and turn it into an array and pass it to the chart.
Needs to be an array, not JSON

That datasource is ouputting JSONP, which is for cross-domain AJAX requests. It's not valid 'raw' JSON because of that extra callback(...) wrapper.
Read up about it here: http://api.jquery.com/jQuery.ajax/ under the 'dataType' section.

As you say in your tags, it's not JSON, it's JSONP. Do not parse it, catch it with a callback. Use jQuery.getScript to do it, and define function callback(data). Inside that function, data should contain the (parsed) object. Also, replace the ? in the URL with callback (or whatever you named your function) - ? is not a valid identifier in JavaScript, so ?([....]) is nonsense.

How to pass variables from an HTTPObject

I'm very, very new to Javascript, and to web programming in general. I think that I'm misunderstanding something fundamental, but I've been unable to figure out what.
I have the following code:
function checkUserAuth(){
var userAuthHttpObject = new XMLHttpRequest();
var url = baseURL + "/userAuth";
userAuthHttpObject.open("POST",url,true);
userAuthHttpObject.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
userAuthHttpObject.onload=function(){
if (userAuthHttpObject.readyState == 4) {
var response = json.loads(userAuthHttpObject.responseText);
return response; //This is the part that doesn't work!
}
};
userAuthHttpObject.send(params);
}
I would love to call it from my page with something like:
var authResponse = checkUserAuth();
And then just do what I want with that data.
Returning a variable, however, just returns it to the userAuthObject, and not all the way back to the function that was originally called.
Is there a way to get the data out of the HttpObject, and into the page that called the function?

Working with AJAX requires wrapping your head around asynchronous behavior, which is different than other types of programming. Rather than returning values directly, you want to set up a callback function.
Create another JavaScript function which accepts the AJAX response as a parameter. This function, let's call it "takeAction(response)", should do whatever it needs to, perhaps print a failure message or set a value in a hidden field and submit a form, whatever.
then where you have "return response" put "takeAction(response)".
So now, takeAction will do whatever it was you would have done after you called "var authResponse = checkUserAuth();"

There are a couple of best practices you should start with before you continue to write the script you asked about
XMLHTTTPRequest() is not browser consistent. I would recommend you use a library such as mootools or the excellent jquery.ajax as a starting point. it easier to implement and works more consistently. http://api.jquery.com/jQuery.ajax/
content type is important. You will have have problems trying to parse json data if you used a form content type. use "application/json" if you want to use json.
true user authorization should be done on the server, never in the browser. I'm not sure how you are using this script, but I suggest you may want to reconsider.
Preliminaries out of the way, Here is one way I would get information from an ajax call into the page with jquery:
$.ajax({
//get an html chunk
url: 'ajax/test.html',
// do something with the html chunk
success: function(htmlData) {
//replace the content of <div id="auth">
$('#auth').html(htmlData);
//replace content of #auth with only the data in #message from
//the data we recieved in our ajax call
$('#auth').html( function() {
return $(htmlData).find('#message').text();
});
}
});

jQuery, Ajax and getting a complete html structure back

I'm new to jQuery and to some extent JavaScript programming. I've successfully started to use jQuery for my Ajax calls however I'm stumped and I'm sure this is a newbie question but here goes.
I'm trying to return in an Ajax call a complete html structure, to the point a table structure. However what keeps happening is that jQuery either strips the html tags away and only inserts the deepest level of "text" or the special characters like <,>, etc get replaced with the escaped ones
I need to know how to turn off this processing of the received characters. Using firebug I see the responses going out of my WebServer correctly but the page received by the user and thus processed by jQuery are incorrect. A quick example will so what I mean.
I'm sending something like this
<results><table id="test"><tr>test</tr></table></results>
what shows up on my page if I do a page source view is this.
<results><table....
so you can see the special characters are getting converted and I don't know how to stop it.
The idea is for the <results></results> to be the xml tag and the text of that tag to be what gets placed into an existing <div> on my page.
Here is the JavaScript that I'm using to pull down the response and inserts:
$.post(url, params, function(data)
{
$('#queryresultsblock').text(data)
}, "html");
I've tried various options other than "html" like, "xml", "text" etc. They all do various things, the "html" gets me the closest so far.

The simplest way is just to return your raw HTML and use the html method of jQuery.
Your result:
<table id="test"><tr>test</tr></table>
Your Javascript call:
$.post(url, params, function(data){ $('#queryresultsblock').html(data) })
Another solution with less control — you can only do a GET request — but simpler is to use load:
$("#queryresultsblock").load(url);
If you must return your result in a results XML tag, you can try adding a jQuery selector to your load call:
$("#queryresultsblock").load(url + " #test");

You can't put unescaped HTML inside of XML. There are two options I see as good ways to go.
One way is to send escaped HTML in the XML, then have some JavaScript on the client side unescape that HTML. So you would send
<results><results><table....
And the javascript would convert the < to < and such.
The other option, and what I would do, is to use JSON instead of XML.
{'results': "<table id="test"><tr>test</tr></table>" }
The JavaScript should be able to extract that HTML structure as a string and insert it directly into your page without any sort of escaping or unescaping.

The other thing you could do is create an external .html file with just your HTML code snippet in it. So create include.html with
<results><table id="test"><tr>test</tr></table></results>
As the contents, then use a jquery .load function to get it onto the page. See it in action here.