Ajax file upload in Wordpress - can't pass FormData

Question

I\'ve made a script which uses $.ajax and FormData to pass two form objects to PHP. One form object is a text and the other is a file. It worked well as a stand-alone script

Answer 1

Works whith any input(one or many simple or multiple), textarea, select in your form (WP 5.0.3)

    $('#form').submit(function(e) {
        e.preventDefault();

        var form = $(this);
        var formdata = (window.FormData) ? new FormData(form[0]) : null;
        var data = (formdata !== null) ? formdata : form.serialize();

        formdata.append("action", "fiu_upload_file");

        $.ajax({
            type: 'POST',
            url: fiuajax.ajaxurl,
            contentType: false,
            processData: false,
            dataType: 'JSON',
            status: 200,
            data: formdata,
            success: function(data){                    
                if(data.error == 'true') {
                    $('.msg').html(data.true);                          
                }
                else {
                    $('.msg').html(data.false); 
                    // your code if you want an action ...                                                                          
                };
            }
        });
    });

and php for only the files

    foreach ($_FILES as $file) :
        if($file['error'] == UPLOAD_ERR_NO_FILE) :
            continue;
        endif;

        $valid_ext = array( 'jpg' , 'jpeg' , 'png' , 'doc' , 'docx' , 'pdf' , 'xls' , 'xlsx');
        $extension_upload = strtolower(  substr(  strrchr($file['name'], '.')  ,1)  );
        if ( in_array($extension_upload,$valid_ext) ) :
            $name_upload = uniqid() . $file['name'];
            $url_insert = trailingslashit( plugin_dir_path( dirname( __FILE__ ) ) ) . 'uploads';
            wp_mkdir_p($url_insert);
            $name_insert = trailingslashit($url_insert) . $name_upload;
            $action = move_uploaded_file($file['tmp_name'],$name_insert);
            $msg_true = 'Upload ok ';
        else :
            $msg_error = 'Upload error';
        endif;
    endforeach;

    $result = !isset($msg_error);
    $msg = array();

    if($result) :
        $msg['error'] = 'true';
        $msg['true'] = $msg_true;
    else :
        $msg['error'] = 'false';
        $msg['false'] = $msg_error;
    endif;



    header('Content-Type: application/json');
    echo json_encode($msg);