check field number

<?php
/*
 *
 * PROJECT NAME    : Field number
 * AUTHOR          : EAKKASIT TUNSAKOOL
 * VERSION CONTROL : GITHUB
 *
 **/
?>
<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>length</title>
	<link rel="stylesheet" type="text/css" href="node_modules/bootstrap/dist/css/bootstrap.min.css">
	<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/font-awesome/4.3.0/css/font-awesome.min.css">
</head>
<body>
	<div class="container">
		<div class="row">
			<div class="col-lg-12 text-center" style="margin-top:10%;">
			<input class="form-group" id="testlength" onkeypress="return checknum();" >
			<p id="test" maxlength="13" style="color:red;"></p>
			<i id="check" class="fa fa-check fa-2x" style="color:green;"></i>
			<p></p>
			<button  type="button" class="btn btn-danger" id="click">Click</button>
			</div>
		</div>
	</div>
	<script type="text/javascript" src="node_modules/jquery/dist/jquery.min.js"></script>
	<script type="text/javascript" src="node_modules/bootstrap/dist/js/bootstrap.min.js"></script>
	<script type="text/javascript">
	$('#check').hide();
		function checknum(e){
		   var keyPressed;
		   if(window.event){ // IE
		      if (event.keyCode < 48 || event.keyCode > 57){
		            event.returnValue = false;
		      }
		   }else{
		      keyPressed = e.which; // Firefox
		       if (keyPressed != 8 && (keyPressed < 48) || (keyPressed > 57)){
		         keyPressed = e.preventDefault();
		      }
		   }
		}
	$(document).on('keyup','#testlength',function(event){
		var value = document.getElementById('testlength').value;
		console.log(value.length);
		limitText(this, 13);
	function limitText(field, maxChar){
	    var ref = $(field),
	        val = ref.val();
	    if ( val.length >= maxChar ){
	        ref.val(function() {
	            return val.substr(0, maxChar);
	        });
	    }
	    if(val.length < 13){
		document.getElementById("test").innerHTML = "กรุณาพิมพ์รหัสบัตรประชาชน 13 หลักครับ";
		}
		if(val.length == 13){
			$("#test").css("color", "green");
			document.getElementById("test").innerHTML = "";
			$('#check').show();
		}else{
			$("#test").css("color", "red");

		}
	}
	});
	$('#click').click(function(){
		var value2 = document.getElementById('testlength').value;
		document.getElementById("test").innerHTML = "id card: "+value2;
	});
	</script>
</body>
</html>