Javascript 函数返回未定义而不是数字

Question

我有两个 Javascript 函数尝试使用 Google Maps API 地理编码查找地址的纬度和经度:

function getLatLon(address) {
    var location = -1;
    geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            var lat = results[0].geometry.location.lat();
            var lon = results[0].geometry.location.lng();
            location = new Array(lat, lon);
            //document.getElementById('results').innerHTML = location[0];
        } else {
            alert("Geocode was not successful.");
        }
    });
    return location;
}

function search() {
    var address = document.getElementById('address').value;
    var location = getLatLon(address);
    document.getElementById('results').innerHTML = location[0];
}

虽然 getLatLon() 内的 location[0] 打印出 #results div 中的正确数字，但 search() 内的 location[0] 返回未定义。您知道为什么会发生这种情况吗？我尝试从 getLatLon() 返回一个纯字符串(“Hello”)，效果很好。

Answer 1

问题是 geocoder.geocode(...) 是异步，因此您无法返回值。尝试像这样:

function getLatLon(address, callback) {
    geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            var lat = results[0].geometry.location.lat();
            var lon = results[0].geometry.location.lng();
            location = new Array(lat, lon);
            callback(location);
        } else {
            alert("Geocode was not successful.");
        }
    });
}

function search() {
    var address = document.getElementById('address').value;
    getLatLon(address, function(location) {
        document.getElementById('results').innerHTML = location[0];
    });
}