Add or replace a query parameter in Javascript

addOrReplaceQueryParameter.js

function addOrReplaceQueryParameter(url, key, value) {
  var keyRegExp = new RegExp('([?&])' + key + '=.*?(&|$)', 'i'),
    // Checks if there are already some query parameters and set separator
    separator = url.indexOf('?') !== -1 ? '&' : '?';

  if (url.match(keyRegExp)) {
    // $1 and $2 will set separators
    return url.replace(keyRegExp, '$1' + key + '=' + value + '$2');
  }
  
  return url + separator + key + '=' + value;
}