[javascript] Checking Value of Radio Button Group via JavaScript?

This may seem silly and downright stupid but I can't seem to figure out how to check the value of a radio button group in my HTML form via JavaScript. I have the following code:

<input type="radio" id="genderm" name="gender" value="male" />
<label for="genderm">Male</label>
<input type="radio" id="genderf" name="gender" value="female" />
<label for="genderf">Female</label>

How do I retrieve the value of gender via JavaScript?

If you wrap your form elements in a form tag with a name attribute you can easily get the value using document.formName.radioGroupName.value.

<form name="myForm">
    <input type="radio" id="genderm" name="gender" value="male" />
    <label for="genderm">Male</label>
    <input type="radio" id="genderf" name="gender" value="female" />
    <label for="genderf">Female</label>
</form>

<script>
    var selected = document.forms.myForm.gender.value;
</script>

To get the value you would do this:

document.getElementById("genderf").value;

But to check, whether the radio button is checked or selected:

document.getElementById("genderf").checked;

In pure Javascript:

var genders = document.getElementsByName("gender");
var selectedGender;

for(var i = 0; i < genders.length; i++) {
   if(genders[i].checked)
       selectedGender = genders[i].value;
 }

update

In pure Javascript without loop, using newer (and potentially not-yet-supported) RadioNodeList :

var form_elements = document.getElementById('my_form').elements;
var selectedGender = form_elements['gender'].value;

The only catch is that RadioNodeList is only returned by the HTMLFormElement.elements or HTMLFieldSetElement.elements property, so you have to have some identifier for the form or fieldset that the radio inputs are wrapped in to grab it first.

Try:

var selectedVal;

for( i = 0; i < document.form_name.gender.length; i++ )
{
  if(document.form_name.gender[i].checked)
    selectedVal = document.form_name.gender[i].value; //male or female
    break;
  }
}

Use document.querySelector() if you want to avoid frameworks (which I almost always want to do).

document.querySelector('input[name="gender"]:checked').value

Without loop:

document.getElementsByName('gender').reduce(function(value, checkable) {
    if(checkable.checked == true) 
        value = checkable.value; 
    return value;
}, '');

reduce is just a function that will feed sequentially array elements to second argument of callback, and previously returned function to value, while for the first run, it will use value of second argument.

The only minus of this approach is that reduce will traverse every element returned by getElementsByName even after it have found selected radio button.