http://diveintohtml5.info/geolocation.html#the-code, https://developers.google.com/maps/documentation/geocoding/

gistfile1.coffee

class Geocoder
  queryGeocodingApi: (options) ->
    if options.coordinates
      formattedLatlng = "#{options.coordinates.latitude},#{options.coordinates.longitude}"
      @.reverseGeocode(latlng: formattedLatlng)
 
  reverseGeocode: (options) ->
    $.ajax
      type: 'GET'
      url: 'https://maps.googleapis.com/maps/api/geocode/json'
      data: { latlng: options.latlng, sensor: false }
      error: (geocodingApiResponse) ->
        return
      success: (geocodingApiResponse) ->
        current_address = geocodingApiResponse.results[0].formatted_address
        $('#search_search').val(current_address)
 
class Location
  getAddress: (geoposition) ->
    geocoder = new Geocoder
    latitude = geoposition.coords.latitude
    longitude = geoposition.coords.longitude
 
    geocoder.queryGeocodingApi(coordinates: { latitude, longitude } )
 
  handleGeolocationFailure: (geoposition) ->
    return
 
$.fn.extend
  user_location: ->
    currentLocation = new Location
    navigator.geolocation.getCurrentPosition(
      currentLocation.getAddress,
      currentLocation.handleGeolocationFailure
    )
 
$ ->
  $('#search_search').user_location()