JSFiddle - React, Tailwind, and code Playground

HTML

<form class="valda_grupper_email_form" method="post">
   <select id="valda_grupper_email" name="" multiple="multiple">
      <option value="1">test1</option>
      <option value="2">test2</option>
      <option value="3">test3</option>
   </select>
</form>

JavaScript

var all_options = [];

$("#valda_grupper_email option").each(function()
{
    all_options.push(this.value);
});

var myJsonString = JSON.stringify(all_options);

$('body').append(myJsonString);