使用Google地图：返回undefined的自定义javascript函数

Question

I'm trying to return the variable coord from GetLocation, but it only returns undefined. Any help appreciated!

var coord = "";
function GetLocation(address) {

    var geocoder = new google.maps.Geocoder();

    geocoder.geocode( { "address": address }, function (results, status) {

        if (status == google.maps.GeocoderStatus.OK) {
            coord = ParseLocation(results[0].geometry.location);

            // This alert shows the proper coordinates 
            alert(coord);
        }
        else{ }

    });

    // this alert is undefined
    alert(coord);
    return coord;
}

function ParseLocation(location) {

    var lat = location.lat().toString().substr(0, 12);
    var lng = location.lng().toString().substr(0, 12);

    return lat+","+lng;
}

Answer 1

When you are returning coords from the outer function it is still in fact undefined . The inner function executes later when the asynchronous operation (if it wasn't asynchronous, the API would just give the result to you normally) is done.

Try passing a callback:

function GetLocation(address, cb) {

    var geocoder = new google.maps.Geocoder();

    geocoder.geocode( { "address": address }, function (results, status) {

        if (status == google.maps.GeocoderStatus.OK) {
            cb(ParseLocation(results[0].geometry.location));
        }
        else{ }

    });
}

You can then use it like so:

GetLocation( "asd", function(coord){
    alert(coord);
});