JSFiddle - React, Tailwind, and code Playground

HTML

<select multiple size=2>
  <option value="volvo">Volvo</option>
  <option value="saab">Saab</option>
  <option value="opel">Opel</option>
  <option value="audi">Audi</option>
</select> <input type="checkbox" id="checkbox" >Select All

<input type="button" id="button" value="check Selected">

JavaScript

$("#checkbox").click(function(){
    if($("#checkbox").is(':checked') ){
        $("select > option").prop("selected","selected");
    }else{
        $("select > option").removeAttr("selected");
     }
});

$("#button").click(function(){
       alert($("select").val());
});