// Strictly check a list of variable types against a list of arguments
  function strict( types, args ) {
  
      // Make sure that the number of types and args matches
      if (  types.length != args.length ) {
          // If they do not, throw a useful exception
          throw "Invalid number of arguments. Expected " + types.length +
              ", received " + args.length + " instead.";
      }
  
      // Go through each of the arguments and check their types
      for ( var i = 0; i < args.length; i++ ) {
          // 
          if ( args[i].constructor != types[i] ) {
              throw "Invalid argument type. Expected " + types[i].name +
                  ", received " + args[i].constructor.name + " instead.";
          }
      }
  }
  
  // A simple function for printing out a list of users
  function userList( prefix, num, users ) {
      // Make sure that the prefix is a string, num is a number,
      // and users is an array
      strict( [ String, Number, Array ], arguments );
  
      // Iterate up to 'num' users
      for ( var i = 0; i < num; i++ ) {
          // Displaying a message about each user
          alert( prefix + ": " + users[i] );
      }
  }