JavaScript - recuperar parametro pasado por GET

<script>

var param1var = getQueryVariable("param1");

function getQueryVariable(variable) {

  var query = window.location.search.substring(1);

  var vars = query.split("&");

  for (var i=0;i<vars.length;i++) {

    var pair = vars[i].split("=");

    if (pair[0] == variable) {

      return pair[1];

    }

  }

  alert('Query Variable ' + variable + ' not found');

}

</script>