parse GET parameters from JS

getparam.js

function getParam(key, qs) {
  const
    results = [],
    reg = new RegExp(`(^|\&)(${key})(=([^&]*))?($|\&)`);
  let
    match = reg.exec(qs = qs||document.location.search.substr(1));
  while(match){
    results.push(match[3]?decodeURIComponent(match[4].replace('+', ' ')):true);
    match = reg.exec(qs = qs.substr(match.index + match[0].length - 1));
  }
  return results;
}

let
  tests = [
    'patata&pata=1&pata',
    'patata&pa=2&pata=1&pata=2'
  ];
for(let test of tests){
  console.log(getParam('pata', test));
}