百度地图JavaScript API获取用户当前经纬度和详细地理位置，反之通过详细地理位置获取当前经纬度

<script type="text/javascript" src="http://api.map.baidu.com/api?v=2.0&ak=您的密钥"></script>

Uncaught TypeError: Cannot read property 'gc' of undefined

<script type="text/javascript">
    var map = new BMap.Map("allmap");//创建Map实例，注意页面中一定要有个id为allmp的div
    var point = new BMap.Point(116.331398,39.897445);//创建定坐标
    map.centerAndZoom(point,12);//// 初始化地图,设置中心点坐标和地图级别

    var geolocation = new BMap.Geolocation();
    var gc = new BMap.Geocoder();//创建地理编码器
    // 开启SDK辅助定位
    geolocation.enableSDKLocation();
    geolocation.getCurrentPosition(function(r){
        if(this.getStatus() == BMAP_STATUS_SUCCESS){
            var mk = new BMap.Marker(r.point);
            map.addOverlay(mk);
            map.panTo(r.point);
            alert('您的位置：' + r.point.lng + ',' + r.point.lat);

            var pt = r.point;   
            map.panTo(pt);//移动地图中心点
            //alert(r.point.lng);//X轴
            //alert(r.point.lat);//Y轴 
 
            gc.getLocation(pt, function(rs){    
                var addComp = rs.addressComponents;
                //alert(addComp.city);
               alert(addComp.province + addComp.city + addComp.district + addComp.street + addComp.streetNumber);    
            });  

        }
        else {
            alert('failed'+this.getStatus());
        }        
    });
</script>

<script type="text/javascript">
var map = new BMap.Map("allmap");
var point = new BMap.Point(116.331398,39.897445);
map.centerAndZoom(point,12);

var geolocation = new BMap.Geolocation();
geolocation.getCurrentPosition(function(r){
    if(this.getStatus() == BMAP_STATUS_SUCCESS){
        var mk = new BMap.Marker(r.point);
        map.addOverlay(mk);
        map.panTo(r.point);
        alert('您的位置：'+r.point.lng+','+r.point.lat);
    }
    else {
        alert('failed'+this.getStatus());
    }        
});
</script>

<script type="text/javasript">
var map = new BMap.Map("allmap");
var point = new BMap.Point(116.331398,39.897445);
map.centerAndZoom(point,12);

function myFun(result){
    var cityName = result.name;
    map.setCenter(cityName);
    alert("当前定位城市:"+cityName);
}
var myCity = new BMap.LocalCity();
myCity.get(myFun); 
</script>

http://api.map.baidu.com/geocoder/v2/?address=长沙市&output=json&ak=您的密钥

$.ajax({
url:"http://api.map.baidu.com/geocoder/v2/?address="+city+"&output=json&ak=您的密钥",
dataType:'jsonp',
processData: false, 
type:'get',
success:function(data){
console.log(data);
if (data.status==0) {
console.log("纬度:"+data.result.location.lat+"经度:"+data.result.location.lng);
}
},
error:function(XMLHttpRequest, textStatus, errorThrown) {
console.log(XMLHttpRequest.status);
console.log(XMLHttpRequest.readyState);
console.log(textStatus);
}});

{"status":0,"result":{"location":{"lng":112.94547319535288,"lat":28.23488939994364},"precise":0,"confidence":12,"comprehension":100,"level":"城市"}}