A module to get a query parameter

querystring.js

define(function() {

  var QueryString = function() {
    // This function is anonymous, is executed immediately and 
    // the return value is assigned to QueryString!
    var query_string = {};
    var query = window.location.search.substring(1);

    // String trailing forward slash if exists
    if (query.charAt(query.length - 1) == "/") {
      query = query.substr(0, query.length - 1);
    }

    var vars = query.split("&");
    for (var i = 0; i < vars.length; i++) {
      var pair = vars[i].split("=");
      // If first entry with this name
      if (typeof query_string[pair[0]] === "undefined") {
        query_string[pair[0]] = pair[1];
        // If second entry with this name
      } else if (typeof query_string[pair[0]] === "string") {
        var arr = [query_string[pair[0]], pair[1]];
        query_string[pair[0]] = arr;
        // If third or later entry with this name
      } else {
        query_string[pair[0]].push(pair[1]);
      }
    }
    return query_string;
  }();

  return QueryString;

});