JSFiddle - React, Tailwind, and code Playground

HTML

<select id="days">
    <option value="10">10</option>
    <option value="20">20</option>
    <option value="30">30</option>
</select

JavaScript

$.extend({
  getUrlVars: function(){
    var vars = [], hash;
    var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
    for(var i = 0; i < hashes.length; i++)
    {
      hash = hashes[i].split('=');
      vars.push(hash[0]);
      vars[hash[0]] = hash[1];
    }
    return vars;
  },
  getUrlVar: function(name){
    return $.getUrlVars()[name];
  }
});

console.log($.getUrlVars());
console.log($.getUrlVar('v'));

$('#days').val($.getUrlVar('v'));