location.js

if ('URLSearchParams' in window) {
  var searchParams = new URLSearchParams(window.location.search);
  searchParams.set("foo", "bar");
  var newRelativePathQuery = window.location.pathname + '?' + searchParams.toString();
  history.pushState(null, '', newRelativePathQuery);
}

for (let n of searchParams.entries()) {
  console.log(n);
}