How to access Query string in javascript?

<script type="text/javascript">

    function getParameterByName()

    {

      var name="QueryStringVariableName";

      var value='';

      name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");

      var regexS = "[\\?&]" + name + "=([^&#]*)";

      var regex = new RegExp(regexS);

      var results = regex.exec(window.location.href);

      if(results == null)

        value= "";

      else

        value= decodeURIComponent(results[1].replace(/\+/g, " "));

    }

    script>