js obj-> json文件（ajax，php）

I currently am getting a 200 green response, however my data is still NOT being written to my json file (i.e. it is still blank)

The JavaScript:

$(function() {
    $('form#saveTemp').submit(function() {
        let savdAta = JSON.stringify($('form#saveTemp').serializeObject());
        //let tempName = savdAta.styleName;
        console.log(savdAta);
        //console.log(JSON.stringify($('form#saveTemp').serializeObject()));

        $.ajax({
          url: './php/data.php',
          type: 'POST',
          contentType: "application/json",  
          data: {
              template: savdAta
          },
          success: function(msg) {
              console.log('data sent to php file, but..');
          }               
        });

        return false;
    });
});

data in console from savdAta is in below format: i.e.

{"styleName":"","fillType":"none","fillTrans":"0"}

PHP:

<?php

header('Content-Type: application/json');

if (!isset($_POST['savdAta']) && !empty($_POST['savdAta'])) {
    $savdAta = $_POST['savdAta'];

    $jsonObject = json_encode($savdAta);
    file_put_contents('./data.json', $jsonObject);
}

Update: Now I have the below, with no errors, and yet still my .json file is blank:

<?php

if (!empty($_POST['template'])) {
    $savdAta = $_POST['template'];

    file_put_contents('./data.json', $savdAta);
}

Your POST variable is template and you're only executing if NOT set AND NOT empty, which is not what you want and would never evaluate to true anyway:

//Not needed
//header('Content-Type: application/json');

if (!empty($_POST['template'])) {
    $savdAta = $_POST['template'];

    //This is already JSON
    //$jsonObject = json_encode($savdAta);
    file_put_contents('./data.json', $savdAta);
}