JSFiddle - React, Tailwind, and code Playground

HTML

<template id="template">
    <form id="shadowForm">
        <input type="text" name="text"/>
        <button type="submit">Submit shadow form</button>
    </form>
</template>


<form id="docForm" >
    <table>
    <tr>
        <td>
            <input type="checkbox" name="checkbox"/>
        </td>
    </tr>
    <tr>
        <td>
            <input type="text" val="" name="text"/>
        </td>
        </tr>
    <tr>
        <td>
            <select name="multiple" multiple="multiple">
                <option>A</option>
                <option>B</option>
                <option>C</option>
            </select>
        </td>
    </tr>
    <tr>
        <td>
            <div id="host"></div>
            <button type="submit"> Submit document Form</button>
        </td>
    </tr>
    </table>
</form>

JavaScript

var template = document.querySelector('template');
var clone = document.importNode(template.content, true);

var root = document.querySelector('#host').createShadowRoot();
root.appendChild(clone);

document.querySelector('button').onclick = function(e) {
    var formValues = $('#docForm').serialize();
    
    alert(formValues);
    return false;
}

document.querySelector('#host').shadowRoot.querySelector('button').onclick = function(e) {
    var form = document.querySelector('#host').shadowRoot.querySelector('#shadowForm');
    
    alert($(form).serialize());
    return false;
}