Ajax POST request in JSON doesn't work - ajax

Question

I try to send an HTTP POST request from ajax to PHP, but I have a syntax error that I don't understand..
Is there anyone who can help me ?
index.php
var key = "keytest";
$.ajax({
url: 'requests.php',
type: 'post',
contentType: 'application/json',
dataType: 'json',
data: '{"uniqueKey" : '+key+'}',
success:function( rep ) {
$('#content').html(rep.content);
},
error:function(a,b,err){
console.log(err);
}
});
requests.php
header('Content-type: application/json');
$uniqueKey = filter_input(INPUT_POST, 'uniqueKey');
$key = "newKey";
$retour = array('key' => $key);
echo json_encode($retour);

Answer 1

Don't build JSON by hand, use JSON.stringify
data: JSON.stringify({uniqueKey: key}),
Php does not populate $_POST(INPUT_POST) when the request body is JSON, only for application/x-www-form-urlencoded or multipart/form-data
To get json you'll have to read it from php://input
$json = file_get_contents('php://input');
$obj = json_decode($json);
$uniqueKey = $obj->uniqueKey;
Also you code only responds with a key value but the ajax request expects a content value. You should change the dataType to text to see if you get back what you expect.
$.ajax({
url: 'requests.php',
type: 'post',
contentType: 'application/json',
dataType: 'text',
data: JSON.stringify({uniqueKey: key}),
success:function( rep ) {
$('#content').html(rep);
},
error:function(a,b,err){
console.log(err);
}
});