Javascript form validation

Radio Button

Set Radio

function setRadio(nami,idx)
{
	var al = document.getElementsByName(nami)
	for(var i=0;i<al.length;i++)
		if(al[i].value==idx)
			al[i].checked = true
}

UnSet Radio

function unSetRadio(nami)
{
	var al = document.getElementsByName(nami)
	for(var i=0;i<al.length;i++)
			al[i].checked = false
}

Get Radio

function getRadio(nami)
{
	var al = document.getElementsByName(nami)
	for(var i=0;i<al.length;i++)
			if(al[i].checked)return al[i].value
	return false;
}

Common Is Selected

Check whether any of an item in a list, radio, check is selected.
This is common for most input controls

function isSelected(ref)
{
	var ch = document.getElementsByName(ref)	
	for(var i=0;i<ch.length;i++)
		if(ch[i].checked)return true;
	return false;		
}

Checkbox validation using jquery

if($('#terms').is(':checked') == false)

Prevent form submit by pressing enter

$('form input').keydown(function (e) {
    if (e.keyCode == 13) {
        e.preventDefault();
        return false;
    }
});

<form ... onkeydown="return event.key != 'Enter';">
Or with jQuery:

$(document).on("keydown", "form", function(event) { 
    return event.key != "Enter";
});

https://stackoverflow.com/questions/895171/prevent-users-from-submitting-a-form-by-hitting-enter/1977126#1977126