The checked property is a Boolean value used to determine whether a radio button is in a checked or unchecked state.
<html>
<head>
<title> Example of the radio checked property</title>
</head>
<body>
<script language="JavaScript">
<!--
function checkButton(){
if(document.form1.button1.checked == true){
alert("Box1 is checked");
} else if(document.form1.button2.checked == true){
alert("Box 2 is checked");
}
}
-->
</script>
<form name="form1">
<input type="radio" name=button1>Box 1
<br>
<input type="radio" name=button2 CHECKED>Box 2
<br>
<INPUT type="button" value="Get Checked" onClick='checkButton()'>
</form>
</body>
</html>