Return PHP array after AJAX call - php

Question

I'm sending an JS object via $.post() and I want to get an array back.
JS
var ajaxData = {action:"createuser"}
$("input[required]").each(function(){
var attr = $(this).attr("name");
ajaxData[attr] = $(this).val();
});
$.post(
daten.ajaxurl,
ajaxData,
function(data){
alert(data[0])
}
)
PHP
//Create a User
add_action('wp_ajax_nopriv_createuser','createuser');
function createuser () {
foreach ($_POST as $key => $value) {
if(empty($value)) {
$type = "error";
$content = "$key is empty";
echo array($type,$content);
wp_die();
}
}
}
What I get as a response is always a string, so it works well if I echo $content.
I've read about that you can use JSON and get it automatically encode if you add DataTaype: "JSON".
But I have no idea how to properly decode it in PHP, tho

Answer 1

I would use the wp_send_json(); function. This is exactly the thing you look for.
And don't forget to put wp_die() at the end.
wp_send_json(): https://codex.wordpress.org/Function_Reference/wp_send_json
wp_die(): https://codex.wordpress.org/Function_Reference/wp_die

Answer 2

You can't just echo an array. In AJAX it's considered default to return JSON objects in requests. What you want to do is make an JSON object from the array. You can use json_encode for that.
http://php.net/json_encode
After that you can use the JSON object in JS/jQuery to do whatever you want to do with it.