<form action="<?php echo $action_url; ?>" method="post" name="adminForm" enctype="multipart/form-data">
<input name="file_order" id="image-file" type="file">
<input type="submit" class="button_confirm" value="" onclick="javascript: return(readURL());">

<script type="text/javascript">
function readURL(form) {
	var size   = 10485760; // bytes
	var file   = input.files[0];
	if (file.size > size) {
		alert('size file large 10 mb');
		return true;
	} else {
	return false;
	}
}
</script>

<form action="<?php echo $action_url; ?>" method="post" name="adminForm" enctype="multipart/form-data" onsubmit="javascript: return(readURL(this));">
	<input name="file_order" id="image-file" type="file">
	<input type="submit" class="button_confirm" value="" >
</form>

	<script type="text/javascript">
		function readURL(form) {
			var size   = 10485760; // bytes
			var file   = form.elements['file_order'].files[0];
			if (file.size > size) {
				alert('size file large 10 mb');
				return false;
			} else {
				alert('Submut')
				return true;
			}
		}
	</script>