如何从嵌套的匿名函数向父函数返回值

Question

我有一个javascript函数,它应该返回一个字符串的地理编码:

    function codeAddress(address) {
    var result = (new google.maps.Geocoder()).geocode( { 'address': address}, function(results, status) {
      if (status == google.maps.GeocoderStatus.OK) {
        return String(results[0].geometry.location.Ya)+','+String(results[0].geometry.location.Za)
      } else {
        return status;
      }
    });
    console.log(result);
    return result
}

但是它返回"未定义".我理解这里的错误,即,因为javascript是异步的,它codeAddress甚至在function(results, status)完全执行之前就从函数返回.但我需要知道这里的解决方案和最佳实践.

Answer 1

由于它是异步的,你应该传递一个处理函数的回调:

function codeAddress(address, callback) {
    (new google.maps.Geocoder()).geocode({
        'address' : address
    }, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            callback(String(results[0].geometry.location.Ya) + ','
                    + String(results[0].geometry.location.Za))
        } else {
            callback(status);
        }
    });
}

codeAddress("test", function(result) {
    // do stuff with result
});

如果你正在使用jQuery,你也可以使用deferred:

function codeAddress(address, callback) {
    var dfd = new jQuery.Deferred();

    (new google.maps.Geocoder()).geocode({
        'address' : address
    }, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
             // trigger success
            dfd.resolve(String(results[0].geometry.location.Ya) + ','
                    + String(results[0].geometry.location.Za));
        } else {
            // trigger failure
            dfd.reject(status); 
        }
    });

    return dfd;
}

codeAddress("some address").then(
    // success
    function(result) {
        // do stuff with result
    },
    // failure
    function(statusCode) {
        // handle failure
    }
);