Uploading multiple files using formData()

You have to get the files length to append in JS and then send it via AJAX request as below

//JavaScript 
var ins = document.getElementById('fileToUpload').files.length;
for (var x = 0; x < ins; x++) {
    fd.append("fileToUpload[]", document.getElementById('fileToUpload').files[x]);
}

//PHP
$count = count($_FILES['fileToUpload']['name']);
for ($i = 0; $i < $count; $i++) {
    echo 'Name: '.$_FILES['fileToUpload']['name'][$i].'<br/>';
}