jquery and json return undefine


I am building a project with a arduino Due that is to be a multiroom thermostat.

To control it, I want to use a web page with the Ethernet shield.

to extract data from arduino to web page, I want to use JSON and Jquery.

Note that I am a real newbe on both c+, HTML or jQuery.
So I follow step by step this video tutorial and tried adapt it to my needs :

jQuery json video turorial

It spit in 2 file the index.htm and main.js.

all the step by step was going good until it can to extrac data from the json data. the json var return ‘undefined’ like this:

here the code:
the index:

<DOCTYPE html>

		<title>Home thermostat</title>
		<h1>jquery get temperature</h1>

		<h2>local temperature</h2>
			<ul id="roomId">


<script src="javascript/jquery.min.js"></script>	
<script src="javascript/main.js"></script>



	var $data = $('#roomId');
		type: 'GET',
		url: '',
		success: function(data) {
			$.each(data, function(i, item){
				$data.append('<li>Room: '+ item.name +' : ' + item.temperature +'</li>');




my json string have check ok with postman so I suppose it could have more with the buffer of ‘$data’ of something like that. but I post my json data anyway.

{"channels" : [{"name":"NAME 0","status":1,"canal":0,"temperature":22.70,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 1","status":0,"canal":1,"temperature":23.02,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 2","status":0,"canal":2,"temperature":22.74,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 3","status":0,"canal":3,"temperature":22.48,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 4","status":0,"canal":4,"temperature":22.55,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 5","status":0,"canal":5,"temperature":22.63,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 6","status":0,"canal":6,"temperature":22.68,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 7","status":0,"canal":7,"temperature":22.68,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 8","status":0,"canal":8,"temperature":0.00,"setPoint":5.00,"permission":0,"percentOut":0},{"name":"NAME 9","status":0,"canal":9,"temperature":-50.00,"setPoint":5.00,"permission":0,"percentOut":0}]}


this is a forum much more focussed on embedded software (only C++, basically). i would recommend to go to stackoverflow for any questions about JQuery or JSON.. your chances are probably much better there.