Send javascript array to php using json - php

Question

This question might be repetitive but i got confused reading all posts relating to this.(sincere apologies!) Basically, I want to send a javascript array to a php file and inturn write the array to a text file . I learnt the best way to go about it is using JSON and AJAX. My code is displays "success" for the ajax part, and also creates a file (php code),but an empty text file.
$('#tabletomodify').on('change','.street',
function (event)
{
event.preventDefault();
var row=( $(this).closest('tr').prop('rowIndex') );
var optionSelected = $("option:selected", this);
var valueSelected = this.value;
var ideSelected= this.id;
var values = [valueSelected];
for ($i=3;$i<row;$i++)
{
var dv="selectstate"+$i;
var dv1=document.getElementById(dv).value;
var sl="selectstreet"+$i;
var sl1=document.getElementById(sl).value;
var po="selectbuilding"+$i;
var po1=document.getElementById(po).value;
var concat=dv1+sl1+po1;
values.push(concat);
}
JSON = JSON.stringify(values);
$.ajax({
url: "get_buildings.php",
type: 'POST',
data: JSON ,
success: function(){
alert("Success!")
}
});
PHP Code:-
<?php
$json = $_POST['JSON'];
$p = json_decode(JSON);
$file = fopen('test.txt','w+');
fwrite($file, $p);
fclose($file);
echo 'success?';
?>

Answer 1

Two flaws:
a) You're not sending your data correctly - it's lacking a field name:
data: {data: JSON}
^^^^---this will be the key in PHP's $_POSt
b) You're using invalid constants in PHP and not even decoding what MIGHT have been the passed in data. You should have:
$p = json_decode($_POST['data']);
^^^^--matching what you have in the `data` field in Javascript.