Untitled

<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="buyA.js">
</script>
<title>Test Page</title>
</head>
<body>
<p id="money">
<script>
document.getElementById("money").innerHTML = "Money: " + money;
</script>
</p>
<p id="cost">
<script>
document.getElementById("cost").innerHTML = "Cost: " + buyA;
</script>
</p>
<input id="Purchase" type="button" value="Purchase" onclick="BuyA();"/>
</body>
</html>

var money = 1000;
var buyA = 500;

function BuyA() {
if (money >= buyA) {
money - buyA;
buyA + 250;
}
else {
window.alert("Not Enough Money")
}
}