Attach event listener through javascript to radio button

I have several radio buttons with the same name. Like this:

<form name="formA">
<input type="radio" name="myradio" value="A"/>
<input type="radio" name="myradio" value="B"/>
<input type="radio" name="myradio" value="C"/>
<input type="radio" name="myradio" value="D"/>
</form>

Now I have to add event listener through javascript to all the radio buttons. If the below pseudocode is wrong, then please tell me how to do it-

var radios = document.forms["formA"].elements["myradio"];
  for(radio in radios) {
    radio.onclick = function() {
        alert(radio.value);
    }
}

Another option is to attach multiple elements to a single event listener by using delegated handlers

You can attach the parent listener to document or any appropriate parent node. Then you can check the event was raised by the appropriate target using the Element.matches() API or anything on event.target

document.getElementById("languages").addEventListener('click', function (event) {
    if (event.target && event.target.matches("input[type='radio']")) {
        // do something here ...
    }
});

This is roughly equivalent to the following jQuery syntax which uses .on() to provide delegation

$("#languages").on("click", "input[type='radio']", function(event) {
    // do something here ...
});

If you want to extend the EventTarget.addEventListener() prototype, you can wrap with your own method:

window.EventTarget.prototype.addDelegatedListener = function(type, delegateSelector, listener) {
    this.addEventListener(type, function (event) {
        if (event.target && event.target.matches(delegateSelector)) {
            listener.call(event.target, event)
        }
    });
}

Then use like this:

document.addDelegatedListener("click", "input[type='radio']", function(event) {
    // do something here ...
});

Demo in Stack Snippets

<!-- begin snippet: js hide: true console: true babel: false --> <!-- language: lang-js -->

// example 1 - regular add event listener
document.getElementById("languages").addEventListener('click', function (event) {
    if ( event.target && event.target.matches("input[type='radio']") ) {
        console.log(event.target.value)
    }
});

// example 2 - reusable delegated listener
window.EventTarget.prototype.addDelegatedListener = function(type, delegateSelector, listener) {
    this.addEventListener(type, function (event) {
        if (event.target && event.target.matches(delegateSelector)) {
            listener.call(event.target, event)
        }
    });
}

let parent = document.getElementById("weekdays")
parent.addDelegatedListener("click", "input[type='radio']", function(event) {
    console.log(this.value)
});

<!-- language: lang-css -->

h3 {
    margin-top: 20px;
    margin-bottom: 10px;
    font-size: 1.1em;
}
code {
    background: #e9e9e9;
    padding: 1px 4px;
    border-radius: 3px;
}
label input {
    vertical-align: text-top;
}

<!-- language: lang-html -->

<h3>Languages <code>addEventListener</code> + <code>Element.matches</code></h3>
<div id="languages">
  <label><input type="radio" name="languages" value="HTML"> HTML </label>
  <label><input type="radio" name="languages" value="JS"> JS </label>
  <label><input type="radio" name="languages" value="CSS"> CSS </label>
</div>

<h3>Weekdays <code>EventTarget.prototype.addDelegatedListener</code></h3>
<div id="weekdays">
  <label><input type="radio" name="days" value="Mon"> Mon </label>
  <label><input type="radio" name="days" value="Tue"> Tue </label>
  <label><input type="radio" name="days" value="Wed"> Wed </label>
</div>

<!-- end snippet -->