Untitled

<!DOCTYPE html>
<html lang= pl >
<head>
<meta charset= utf-8 >
<title></title>
<script>
"use strict";
var zp1, zp2, zbt1, ztxt1, zpole, zobw, x;
window.onload = function (){
	ztxt1 = document.getElementById("txt1");
	zbt1 = document.getElementById("bt1");
	zp1 = document.getElementById("p1");
	zp2 = document.getElementById("p2");

	zbt1.onclick = function (){
		if((ztxt1.value == "") || (isNaN(ztxt1.value))){
			alert("wpisz liczbe w 1 polu");
			ztxt1.value = "";
			ztxt1.focus();
			return;
		}


		x = parseFloat(ztxt1.value);

		zpole = Math.round(Math.PI*x*x);
		zobw = Math.round(2*Math.PI*x);

		zp1.innerHTML = "Pole wynoci: "+zpole+"m<sup>2</sup>, a obwód: "+zobw+"m.";
		zp2.innerHTML = "Pole wynoci: "+zpole+"m<sup>2</sup>.";
		zp2.innerHTML = zp2.innerHTML+" <br>Obwód wynosi: "+zobw+"m.";
	}
}
</script>
</head>
<body>
<p><h1>JS z e14-01-2015 pole i obwód koła</h1></p>
	Długość promienia = <input type=text  id="txt1" >w metrach.<br /><br />

	<input type=button id="bt1" value="oblicz pole i obwó prostokąta" >

<br><br>
<p id=p1>
<p id=p2>
</p>
</body>
</html>