Radio button policy - forms

Question

Do radio buttons have policy of setting default value? I want to create form where are radio buttons and it is required value. What is better to select one on show form or show all and put error message(if any radio button, not selected on submit)?

Answer 1

You can select a default radio value by using checked
<input type=radio name=r1 value="1" checked>
<input type=radio name=r1 value="2">
Here default value is set to 1, v should use checked keyword.
It is better to set default radio button option.
Suppose if u dont want to use default radio button selection You can call a js function(using onsubmit()). Like this
<form id="ID" method="post" action="servleName" onSubmit="return validateOption()">
<input type=radio name=r1 value="1" >A</input>
<input type=radio name=r1 value="2">B</input>
<input type="submit" value="Submit"><span id="error" style="display:none;"></span>
</form>
Your script goes here to validate whether option selected or not,Submission of page is possible only if onsubmit=true ie if validateOption() returns true.
<script>
function validateOption()
{
var group=document.getElementsByName("r1");
for ( var i = 0; i < group.length; i++)
{
if (group[i].checked)
return true;
}
// else you can show error message like this
document.getElementById("error").innerHTML="Please enter your choice";
return false;
}
</script>