[英]javascript function is returning undefined
我正在尝试实现谷歌地图,我遇到的问题是,当我调用 function getLatLng 时,它返回一个未定义的值,我不知道为什么。
initialize();
var map;
var geocoder;
function initialize() {
geocoder = new google.maps.Geocoder();
var address = "Rochester, MN";
var myLatLng = getLatLng(address);
console.log("myLatLng = "+myLatLng);
}
function getLatLng(address) {
var codedAddress;
geocoder.geocode({'address': address}, function(results, status) {
if(status == google.maps.GeocoderStatus.OK) {
codedAddress = results[0].geometry.location;
console.log("codedAddress 1 = "+codedAddress);
} else {
alert("There was a problem with the map");
}
console.log("codedAddress 2 = "+codedAddress);
});
console.log("codedAddress 3 = "+codedAddress);
return codedAddress;
}
在萤火虫控制台中,这是我按以下确切顺序获得的 output:
codedAddress 3 = undefined
myLatLng = undefined
codedAddress 1 = (44.0216306, -92.46989919999999)
codedAddress 2 = (44.0216306, -92.46989919999999)
为什么 codedAddress 3 和 myLatLng 首先出现在控制台中?
geocode
是异步的(即它向 Google 的服务器发送请求),因此您需要将回调 function 传递给getLatLng
,而不是让它立即返回:
function getLatLng(address, callback) {
var codedAddress;
geocoder.geocode({'address': address}, function(results, status) {
if (status == google.maps.GeocoderStatus.OK) {
codedAddress = results[0].geometry.location;
console.log("codedAddress 1 = "+codedAddress);
} else {
alert("There was a problem with the map");
}
console.log("codedAddress 2 = "+codedAddress);
callback(codedAddress);
});
}
您缺少用于初始化 function 的结束}
。
以下是我通过 Google 地图文档所做的工作:
var geocoder;
var map;
function initialize() {
geocoder = new google.maps.Geocoder();
var address = "Rochester, MN";
var latlng = codeAddress(address);
var myOptions = {
zoom: 8,
center: latlng,
mapTypeId: google.maps.MapTypeId.ROADMAP
}
map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
}
function codeAddress(address) {
geocoder.geocode( { 'address': address}, function(results, status) {
if (status == google.maps.GeocoderStatus.OK) {
map.setCenter(results[0].geometry.location);
var marker = new google.maps.Marker({
map: map,
position: results[0].geometry.location
});
} else {
alert("Geocode was not successful for the following reason: " + status);
}
});
}
这是一个 jsFiddle 来查看它的实际效果。 显然,如果需要,您可以将其更新为使用 jQuery。
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