Develop Reference

Passing Value from C++ to Javascript

i have a c++ file which reads values from a sensor and I want to display those values on a website dynamically. So Im looking for a way to pass these values(integers) from my cpp file to an javascript which displays them on the site.
My first, simple try was to write the values into a js file as variables every second from my cpp script. The Js then uses this file as a source and displays its variables on the site:
cpp:
fprintf(file, "var mx=%d, my=%d, mz=%d, ax=%d, ay=%d, az=%d, gx=%d, gy=%d, gz=%d;\n",
imu.raw_m[0], imu.raw_m[1], imu.raw_m[2], // M = Magnetometer
imu.raw_a[0], imu.raw_a[1], imu.raw_a[2], // A = Accelerometer
imu.raw_g[0], imu.raw_g[1], imu.raw_g[2] // G = Gyroscope
);
html/js:
<script src="./imu.js" type="text/javascript"></script>
The Problem now is of course, that I need to refresh the page all the time, because the imu.js file is cached by the website.
I'd rather have a way to directly pass to integers from the cpp file to the js script. I read something about json or Googles V8 script. But I'd like to hear your suggestions first.
By the way, Im running this on a raspi, if this is important.
Thanks for your help
EDIT:
I'm goning to try it with a mysql database, in which my cpp file writes the data from the sensor with Connector/c++ from http://dev.mysql.com/doc/connector-cpp/en/ and my website reads them.

You could compile your C++ code into a Node.js plugin, you can then register a JavaScript function with your plugin which the C++ calls when it updates the value. That way you can pass values directly from C++ into Javascript in a managed and controlled way.
Node.js has the added benefit of being able to host your webpage and do all the Websocket and HTTP stuff that can be a pain in C++.

You do not have to refresh if your script is smart about how to access the data file! In case you do have a webserver at hand: Take care that your data file is accessible by your webserver and then let your script request the file via ajax (link to w3schools)

I'm doing something similar on a BeagleBone Black. With websocketd you can turn pretty much any program into a websocket endpoint and then send data via stdin and stdout commands. This would be a particularly good solution for you since websockets are designed to handle information that's constantly changing.

Write a line to javascript file

Im using a array to display some images in a website:
var paintingImages;
paintingImages =
[
{
url: 'images/objects/ron.jpg',
alt: 'ron'
}
];
This js code is written in paintings.js and my main js code is written in the file main.js
I have made this website for a artist and I want to give him the opportunity to login and add pictures to his website. I'm not that good with php, but adding images to a ftp in a folder is no problem.
Because I'm using a array for retrieving the images, I need to be able to add items to the array.
This is the part where I'm stuck. I don't know how to edit a existing js file, so the next time I open the website, the items (images) will been shown.
Activexobject is not a option because it's only possible in IE.
In summary:
I need to add a item to a array
I need to save this into the file, so the next time the website opens, it will be shown
I'm not verry good with php, I prefer javascript
Can't use Activexobject because of the use of multiple browsers

You can not simply modify a javascript file sitting on the server from browser side javascript.
You need to implement some server side logic.
If you don't like PHP, but like JavaScript, check out NodeJS for example.
With Node you should be able to build some lightweight serverside logic to modify your json array file with additional images.

You would need to change your logic .. You need to send this data to server anyhow . and when you load your next time take it back from server and update your webpage accordingly. I would suggest use any javascript MVC framework like backbone, angular.js. it will help you.

Use a database.
Save it to a database server (You figure this out, could be via forms, xhr, websockets, etc.).
On page load, load the correct data for the current user.
Create the $userPaintings array (call it what you want) from the user data in PHP.
Then simply output a JS object in the page with PHP:
<script>
var paintingImages = <?php json_encode($userPaintings); ?>
</script>

Save javascript output to a file?

I have php made website. It runs on windows machine. I have a javascript that i have tested that gets me the adobe version used by clients. The problem is that by running the code I'm able to retrieve the Adobe Reader version but cannot saved the output to a file on my server end.
Here is the Javascript code. I took this code from sister stackexchange website.
http://jsfiddle.net/EGbY5/3/
What is the best way to save this information from js? Should i use js or any other scripting? I read this from google that you cannot use js to save files on server? If this is true is there any other way.

I would suggest using AJAX (or a form, if you want the user to explicitly know this is happening) to send a request to your server side code detailing the information you have collected with the script.
The advantage of AJAX is that you can do all of this without the user being explicitly aware of it. The disadvantage is that you rely on their browser supporting Javascript, but since you are already collecting information using Javascript this problem is mute.

Ajax'll do it.
JavaScript source:
var adobeVersion = CheckAdobeVersion();
$.post("script.php", {version: adobeVersion}, function(){});
PHP source:
<?php
$version = $_POST['version'];
write all text to a file("my file.txt") // Pseudo code...
?>

How to let js make a request from python and preserve the loaded site in place when answered by python

Opening a site economizing the data load I seem to run into a need to add more data from Python occasionally. I use Python with CherryPy and Mako for loading a site.
So, how can I make a JavaScript request from Python to pass me some more data, once the site was loaded already. I want to do that without moving away from the site. I know that JavaScript can do all sorts of things, but Python can be a real muscle for me with better debugging features.
Now, I'm not keen on Ajax. I know nothing about it and I have that fear factor that it would be quite complex.
TIA
Dennis

For example you can make with jQuery like this,
in controller you return rendered template:
def some_html():
return render('my_template.tpl')
and in the client side you can use jQuery
<script type="text/javascript">
('#result_from_server').load('/some_html');
</script>
,where result_from_server its can be id of wrapper div like
<div id="result_from_server"></div>
and /some_html, url for call your some_html() function.
Very good resurce for quick start with jQuery jqapi.com

How to make a javascript like Disqus or IntenseDebate

I want to make an app that can display on any webpage, just like how Disqus or IntenseDebate render on articles & web pages.
It will display a mini-ecommerce store front.
I'm not sure how to get started.
Is there any sample code, framework, or design pattern for these "widgets"?
For example, I'd like to display products.
Should I first create a webservice or RSS that lists all of them?
Or can one of these Ajax Scripts simply digest an XHTML webpage and display that?
thanks for any tips, I really appreciate it.

Basically you have two options - to use iframes to wrap your content or to use DOM injection style.
IFRAMES
Iframes are the easy ones - the host site includes an iframe where the url includes all the nessessary params.
<p>Check out this cool webstore:</p>
<iframe src="http://yourdomain.com/store?site_id=123"></iframe>
But this comes with a cost - there's no easy way to resize the iframe considering the content. You're pretty much fixed with initial dimensions. You can come up with some kind of cross frame script that measures the size of the iframe contents and forwards it to the host site that resizes the iframe based on the numbers from the script. But this is really hacky.
DOM injection
Second approach is to "inject" your own HTML directly to the host page. Host site loads a <script> tag from your server and the script includes all the information to add HTML to the page. There's two approaches - first one is to generate all the HTML in your server and use document.write to inject it.
<p>Check out this cool webstore:</p>
<script src="http://yourdomain.com/store?site_id=123"></script>
And the script source would be something like
document.write('<h1>Amazing products</h1>');
document.write('<ul>');
document.write('<li>green car</li>');
document.write('<li>blue van</li>');
document.write('</ul>');
This replaces the original <script> tag with the HTML inside document.write calls and the injected HTML comes part of the original page - so no resizing etc problems like with iframes.
<p>Check out this cool webstore:</p>
<h1>Amazing products</h1>
<ul>
<li>green car</li>
<li>blue van</li>
</ul>
Another approach for the same thing would be separating to data from the HTML. Included script would consist of two parts - the drawing logic and the data in serialized form (ie. JSON). This gives a lot of flexibility for the script compared to the kind of stiffy document.write approach. Instead of outpurring HTML directly to the page, you generate the needed DOM nodes on the fly and attach it to a specific element.
<p>Check out this cool webstore:</p>
<div id="store"></div>
<script src="http://yourdomain.com/store_data?site_id=123"></script>
<script src="http://yourdomain.com/generate_store"></script>
The first script consists of the data and the second one the drawing logic.
var store_data = [
{title: "green car", id:1},
{title: "blue van", id:2}
];
The script would be something like this
var store_elm = document.getElementById("store");
for(var i=0; i< store_data.length; i++){
var link = document.createElement("a");
link.href = "http://yourdomain.com/?id=" + store_elmi[i].id;
link.innerHTML = store_elmi[i].title;
store_elm.appendChild(link);
}
Though a bit more complicated than document.write, this approach is the most flexible of them all.
Sending data
If you want to send some kind of data back to your server then you can use script injection (you can't use AJAX since the same origin policy but there's no restrictions on script injection). This consists of putting all the data to the script url (remember, IE has the limit of 4kB for the URL length) and server responding with needed data.
var message = "message to the server";
var header = document.getElementsByTagName('head')[0];
var script_tag = document.createElement("script");
var url = "http://yourserver.com/msg";
script_tag.src = url+"?msg="+encodeURIComponent(message)+"&callback=alert";
header.appendChild(script_tag);
Now your server gets the request with GET params msg=message to the server and callback=alert does something with it, and responds with
<?
$l = strlen($_GET["msg"]);
echo $_GET["callback"].'("request was $l chars");';
?>
Which would make up
alert("request was 21 chars");
If you change the alert for some kind of your own function then you can pass messages around between the webpage and the server.

I haven't done much with either Disqus or IntenseDebate, but I do know how I would approach making such a widget. The actual displaying portion of the widget would be generated with JavaScript. So, say you had a div tag with an id of commerce_store. Your JavaScript code would search the document, when it is first loaded (or when an ajax request alters the page), and find if a commerce_store div exists. Upon finding such a container, it will auto-generate all the necessary HTML. If you don't already know how to do this, you can google 'dynamically adding elements in javascript'. I recommend making a custom JavaScript library for your widget. It doesn't need to be anything too crazy. Something like this:
window.onload = init(){
widget.load();
}
var widget = function(){
this.load = function(){
//search for the commerce_store div
//get some data from the sql database
var dat = ajax('actions/getData.php',{type:'get',params:{page:123}});
//display HTML for data
for (var i in dat){
this.addDatNode(dat[i]);
}
}
this.addDatNode = function(stuff){
//make a node
var n = document.createElement('div');
//style the node, and add content
n.innerHTML = stuff;
document.getElementById('commerce_store').appendNode(n);
}
}
Of course, you'll need to set up some type of AJAX framework to get database info and things. But that shouldn't be too hard.
For Disqus and IntenseDebate, I believe the comment forms and everything are all just HTML (generated through JavaScript). The actual 'plugin' portion of the script would be a background framework of either ASP, PHP, SQL, etc. The simplest way to do this, would probably just be some PHP and SQL code. The SQL would be used to store all the comments or sales info into a database, and the PHP would be used to manipulate the data. Something like this:
function addSale(){ //MySQL code here };
function deleteSale(){ //MySQL code here };
function editSale(){ //MySQL code here };
//...
And your big PHP file would have all of the actions your widget would ever need to do (in regards to altering the database. But, even with this big PHP file, you'll still need someway of calling individual functions with your ajax framework. Look back at the actions/getData.php request of the example JavaScript framework. Actions, refers to a folder with a bunch of PHP files, one for each method. For example, addSale.php:
include("../db_connect.php");
db_connect();
//make sure the user is logged in
include("../authenticate.php");
authenticate();
//Get any data that AJAX sent to us
var dat = $_GET['sale_num'];
//Run the method
include("../PHP_methods.php");
addSale(dat);
The reason you would want separate files for the PHP_methods and run files, is because you could potentially have more than one PHP_methods files. You could have three method API's, one for displaying content, one for requesting content, and one for altering content. Once you start reusing your methods more and more, its best to have them all in one place. Rewritten once, rewritten everywhere.
So, really, that's all you'd need for the widget. Of course, you would want to have a install script that sets up the commerce database and all. But the actual widget would just be a folder with the aforementioned script files:
install.php: gets the database set up
JavaScript library: to load the HTML content and forms and conduct ajax requests
CSS file: for styling the HTML content and forms
db_connect: a generic php script used connect to the database
authenticate: a php script to check if a user is logged in; this could vary, depending on whether you have your own user system, or are using gravitars/facebook/twitter/etc.
PHP_methods: a big php file with all the database manipulation methods you'd need
actions folder: a bunch of individual php files that call the necessary PHP methods; call each of these php files with AJAX
In theory, all you'd have to do would be copy that folder over to any website, and run the install.php to get it set up. Any page you want the widget to run on, you would simply include the .js file, and it will do all the work.
Of course, that's just how I would set it up. I assume that changes in programming languages, or setup specifics will vary. But, the basic idea holds similar for most website plugins.
Oh, and one more thing. If you were intending to sell the widget, it would be extremely difficult to try and secure all of those scripts from redistribution. Your best bet would be to have the PHP files on your own server. The client would need to have their own db_connect.php, that connects to their own database and all. But, the actual ajax requests would need to refer to the files on your remote server. The request would need to send the url of the valid db_connect, with some type of password or something. Actually, come to think of it, I don't think its possible to do remote server file sharing. You'd have to research it a bit more, 'cuz I certainly don't know how you'd do it.

I like the Azmisov's solution, but it has some disadvantages.
Sites might not want your code on their servers. It'd be much better if you would switch from AJAX to loading scripts (eg. jQuery's getJSON)
So I suggest:
Include jquery hosted on google and a short jquery code from your domain to the client sites. Nothing more.
Write the script with cross-domain calls to your server (through getJSON or getScript) so that everything is fetched directly and nothing has to be inctalled on the client's server. See here for examples, I wouldn't write anything better here. Adding content to the page is easy enough with jQuery to allow me not mentioning it here :) Just one command.
Distribute easily by providing two lines of <script src= ... ></script>