JSFiddle - React, Tailwind, and code Playground

HTML

<input type='checkbox' class='Company' data-companyid='1'> 1<br>
<input type='checkbox' class='Company' data-companyid='2'> 2<br>
<input type='checkbox' class='Company' data-companyid='3'> 3<br>

JavaScript

// SET BY CLASS
$Company = $("input.Company");

// GET COMPANY LIST 

function getCompanyList() {
    var len = $Company.length;
    alert(len );
}
$Company.change(getCompanyList);