var geocoder;
  var mini_map;
  function initialize() {
    geocoder = new google.maps.Geocoder();
    var myOptions = {
      zoom: 15,
      mapTypeId: google.maps.MapTypeId.ROADMAP
    }
    mini_map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
    codeAddress(mini_map, "google_map_postcode")
  }

  function codeAddress(map, element_id) {
    var address = document.getElementById(element_id).value;
    if (geocoder) {
      geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
          map.setCenter(results[0].geometry.location);
          var marker = new google.maps.Marker({
              map: map,
              position: results[0].geometry.location
          });
        } else {
          alert("Geocode was not successful for the following reason: " + status);
        }
      });
    }
  }
 window.onload=initialize;