Update query string value with Javascript (author: Anthony Vipond)

update_query_string_value.html

  <select class="filter">
    <option>Results Shown</option>
    <option>20</option>
    <option>30</option>
    <option>50</option>
    <option>100</option>
  </select>

  <script>
  // This example is for a 'Results per page' dropdown
  // It will check if this query string var exists, if not, it adds it
  // If is exists, and its the same as the options text value, it does nothing
  // If it exists and is different than the option text value, we redirect whilst updating query string value
  
  // this function not written by me :)
  function getParameterByName(name) {
	    name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
	    var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
	        results = regex.exec(location.search);
	    return results == null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
	}
	
  // Change results shown per page
  $('select.filter').change(function() {
  	var text = $(this).find(":selected").text();
  	if (location.search) {
  		var limit = getParameterByName('limit');
  		if (/[?&]limit=/.test(location.href)) {
  			if (limit !== text) {
  				location = location.search.replace('limit=' + limit, 'limit=' + text);
  			} 
  		}
  	} else {
  		location.pathname + '?limit=' + text;
  	}
  }); 
  </script>