<script>
var ret = prompt("enter something","abc");
if (ret == null)
{
alert("cancelled");
}
else if (ret.replace(/^\s+|\s+$/g,"") == "")
alert("empty");
else
alert(ret);
</script>
var ret = prompt("enter something","abc");
if (ret == null)
{
alert("cancelled");
}
else if (ret.replace(/^\s+|\s+$/g,"") == "")
alert("empty");
else
alert(ret);
</script>
...