通过Ajax将JS数组传递给PHP

I have an array in javascript and I need to convert it into PHP array. So I have this code and I have tried other codes too but no one has worked. Here is the code:

<!DOCTYPE html>
<html>
<head>
    <title></title>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
</head>
<body>
    <div id="res" style="border: 1px solid black; width: 400px; height: 200px;"></div>
    <br>
    <input type="file" name="img[]" id="img" multiple>
    <input type="submit" name="submit" id="submit">
    <script>
        var array = new Array();
        $('#img').change(function() {
            var img = $('#img').val().split('\\').pop();
            array.push(img);
            document.getElementById('res').innerHTML = array;
        });
        $('#submit').click(function() {
            var send_data = JSON.stringify(array);
            $.ajax({
                type: "POST",
                enctype: "multipart/form-data",
                url: "test.php",
                data: {send_data:send_data},
                datatype: "JSON",
                success: function(data) {
                }
            });
        });
    </script>
</body>
</html>

And my test.php

<?php 
$data = $_POST['send_data'];
$decoded = json_decode($data, true);
var_dump($decoded);
?>

</div>

HTML && Javascript sample code:

function validateForm() {
let formData = {
        'name': $('input[name=name]').val(),
        'email': $('input[name=email]').val(),
        'message': $('textarea[name=message]').val()
    };
    //Prevent page from refresh after sending message (ajax)
    $.ajax({
        url: "./assets/php/contact_me.php",
        type: "POST",
        data: formData,
        success: function (data, textStatus, jqXHR) {
            if (data.code)
                $('#status').text(data.message);
        },
        error: function (jqXHR, textStatus, errorThrown) {
            $('#status').text("Error");
        }
    });
}
<a class="btn" onclick="validateForm()">Send Message</a>

<!-- Status text -->
<div id="status" class="text-danger pb-2"></div>

PHP Code:

<?php

$name = $_POST['name'];
$email = $_POST['email'];
$message = $_POST['message'];

header('Content-Type: application/json');
if (strlen($name) < 3){
    print json_encode(array('message' => 'Name is too short', 'code' => 0));
    exit();
}
if ($email === ''){
    print json_encode(array('message' => 'Email cannot be empty', 'code' => 0));
    exit();
} else {
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        print json_encode(array('message' => 'Email format invalid.', 'code' => 0));
        exit();
    }
}
if (strlen($message) < 5){
    print json_encode(array('message' => 'Message is too short', 'code' => 0));
    exit();
}
print json_encode(array('message' => 'successfull!', 'code' => 1));
exit();

</div>

I have an array in javascript and I need to convert it into PHP array.

You can transform a javascript array (call it myDataAsJSArray) into a JSON string, before POST-ing:

let myDataAsJSON = JSON.stringify('myDataAsJSArray');

After POST-ing, you can transform the JSON string into a PHP array:

$My_Data_As_PHP_Array = json_decode($_POST['myDataAsJSON'], TRUE);

Note that if you omit the optional TRUE parameter immediately above, PHP will transform your JSON into a PHP Object, rather than a PHP Array.

Further Reading: