How get AJAX to Post JSON data into div - php

Question

I'm new Jquery and AJAX and I've really been struggling with the syntax I've been trying to use other tutorials as reference but nothing seems to work. I feel I have the right idea but syntax is wrong somewhere please help.
Here is the Ajax side
var var_numdatacheck = <?php echo $datacheck; ?>;
var var_numcheck = parseInt(var_numdatacheck);
function activitycheck(){
$.ajax({
type: 'POST',
url: 'feedupdate.php',
data: {function: '3test', datacheck: var_numcheck},
dataType: "json",
success: function(data) {
var json = eval('(' + data + ')');
$('#datacheck').html(json['0']);
var var_numcheck = parseInt(msg);
//setTimeout('activitycheck()',1000)},
error:function(msg) {
console.log(msg);
}
});
}
$(document).ready(function() {
activitycheck();
});
Here is the php the AJAX calls
<?php
require "dbc.php";
$function = $_POST['function'];
$datacheck = $_POST['datacheck'];
$search="SELECT * FROM Feedtest ORDER BY id DESC";
$request = mysql_query($search);
$update= mysql_fetch_array($request);
$updateid = $update['id'];
$updatecheck = mysql_num_rows($request);
$data = array();
if ($function == $datacheck){
echo $updatecheck;
echo $datacheck;
}
if ($function == "3test" && $updatecheck > $datacheck ) {
$updatesearch="SELECT * FROM Feedtest WHERE id = '$updateid' ORDER BY id DESC";
$updatequery = mysql_query($updatesearch);
$data['id'] = $updateid;
while ($row = mysql_fetch_array($updatequery))
{
?>
<?php $data[]= $row['First Name']; ?>
<?php
}
echo json_encode($data);
}
?>
</div>
</ul>

Answer 1

first of all ,always use JSON.parse(data) instead of eval.It is considereda a good practice.
second thing is always try to debug your code by checking it in console or alerting.In your context,this is what is happening-:
$.ajax({
type: 'POST',
url: 'feedupdate.php',
data: {function: '3test', datacheck: var_numcheck},
dataType: "json",
success: function(data) {
var data = eval('(' + data + ')');
console.log("myData"+data)//debugging.check the pattern so that you can acces it the way you want!!!
for(var i=0;i< data.length;i++)
{
alldata += "<li>"+data[i][0]+"<li><hr>";
}
$('#datacheck').html(alldata);
});
}
For JSON.parse:
success: function(data) {
var data = JSON.parse(data);
console.log("myData"+data)//debugging.check the pattern so that you can acces it the way you want!!!
for(var i in data)
{
alldata += "<li>"+data[i].First Name+"<li><hr>";
}
$('#datacheck').html(alldata);
});