create and modify json string - php

Question

This is my first time, that I am working with json.
This is the situation:
I get data via php from my mysql database and store this into a php array:
$statement = $mysqli->prepare("SELECT chatToken, lastMessageID FROM chat")
$statement->execute();
$result = $statement->get_result();
while($row = $result->fetch_object()) {
$chatData[$row->chatToken] = $row->lastMessageID;
}
Now I would like to get this in a jquery function:
I tried this:
var chatData = '<? echo json_encode($chatData); ?>'
myFunction(chatData)
function myFunction(chatData) {
console.log(chatData)
// OUTPUT: {"tgv5pxfjsDGXA3JcEYVM":88,"a9gxNZ7HzfcJXQsWCtAp":99}
$.ajax({
type: "POST",
url: "getData.php",
data: 'chatData='+chatData,
dataType: 'json',
}).done(function(result) {
console.log(result);
// Please look the Picture below for output
})
}
Output of console.log(result)
getData.php
<?php
$chatData = json_decode($_POST['chatData']);
$message = array();
foreach($chatData AS $chatToken => $lastMessageID) {
$statement = $mysqli->prepare("SELECT * FROM `messages` WHERE `chatToken` = ? AND `ID` > ?")
$statement->bind_param("ss", $chatToken, $lastMessageID);
$statement->execute();
$result = $statement->get_result();
while($row = $result->fetch_object()) {
$message[] = array(
"lastMessageID" => $row->ID,
"chatToken" => $row->chatToken,
);
}
$statement->close();
}
echo json_encode($message);
?>
So far so good.
But now I would like to replace / update my var chatData:
{"tgv5pxfjsDGXA3JcEYVM":88,"a9gxNZ7HzfcJXQsWCtAp":99}
with values from the result. Finally it have to be:
{"tgv5pxfjsDGXA3JcEYVM":188,"a9gxNZ7HzfcJXQsWCtAp":99}
How can I realize it?

Answer 1

As chatData is JSON (a string), you can:
parse it into an object JSON.parse
make the change
convert it back to a string JSON.stringify
// result from ajax call, jquery converts this from the php json to an object/array
var result = [{chatToken:"tgv5pxfjsDGXA3JcEYVM",lastMessageID:188}];
// string from `var chatData = <?php ...` as JSON
var chatData = '{"tgv5pxfjsDGXA3JcEYVM":88,"a9gxNZ7HzfcJXQsWCtAp":99}';
// convert string to object
var data=JSON.parse(chatData);
// use the first result array ([0]) chatToken to update chatData
data[result[0].chatToken] = result[0].lastMessageID;
// convert back to JSON (string)
chatData = JSON.stringify(data);
// show result
console.log(chatData);
In your case, I'd recommend converting chatData to an object at the start
var chatData = JSON.parse('<? echo json_encode($chatData); ?>');
and then using it as an object, then convert to json(string) only as needed (in the ajax post)
data: 'chatData='+JSON.stringify(chatData),