Radio button validation + iodine.js

your.html

<label for="password">Plan</label>
<input name="plan" type="radio" id="pro" value="pro" x-bind:class="{'invalid':plan.errorMessage}" data-rules='["requiredChoice:plan"]' data-server-errors='[]'>
<input name="plan" type="radio" id="basic" value="basic" x-bind:class="{'invalid':plan.errorMessage}" data-rules='["requiredChoice:plan"]' data-server-errors='[]'>
<p class="error-message" x-show.transition.in="plan.errorMessage" x-text="plan.errorMessage"></p>

your.js

Iodine.addRule("requiredChoice", (value, name) => {
 return document.querySelector('input[name="' + name + '"]:checked') != null;
});
Iodine.messages.requiredChoice = "Please select one of these options";