Question

Background

As per the WHATWG someForm.elements should return a HTMLFormElementsCollection.

A HTMLFormElementsCollection returns a RadioNodeList if multiple elements share the same name.

The RadioNodeList has special value semantics where it returns the value of the first checked radio list in the nodelist.

This would allow the following answer to work if it were implemented

I naively attempted a polyfill that is based on host objects being well behaved (as per WebIDL), which they are clearly not.

Question

What is an alternative efficient implementation for this polyfill whilst we wait for browsers to become either RadioNodeList or WebIDL compliant?

Example Reference code

<form name="myform">
    <input type="radio" name="foo" value="10" /> foo 
    <input type="radio" name="foo" value="30" /> bar 
</form>

var myform = document.forms.myform;

var radio = myform.elements.foo;
var price = radio.value;

Naive attempt reference code

(function () {
    var pd = Object.getOwnPropertyDescriptor(HTMLFormElement.prototype, "elements"),
        getElements = pd.get;

    pd.get = get;

    Object.defineProperty(HTMLFormElement.prototype, "elements", pd);

    function get() {
        var elements = getElements.call(this);

        if (elements.length) {
            Object.defineProperty(elements, "value", {
                get: getRadioNodeListValue,
                set: setRadioNodeListValue,
                configurable: true
            });
        }

        return elements;
    }

    function getRadioNodeListValue() {
        for (var i = 0, len = this.length; i < len; i++) {
            var el = this[i];
            if (el.checked) {
                return el.value;   
            }
        }
    }

    function setRadioNodeListValue(value) {
        for (var i = 0, len = this.length; i < len; i++) {
            var el = this[i];
            if (el.checked) {
                el.value = value;
                return;   
            }
        }    
    }
}());

Answer 1

If you can accept bolting the value getter onto NodeList then the following should work

RadioNodeList polyfill

Credit to @@Esailija

you could also just add .value to NodeList prototype