获取回调函数的结果

Question

我有这个功能。我似乎不明白它是如何工作的。因为我想使用此函数返回returnlatlang。但它根本行不通。

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

function codeAddress(address) {
    var returnlatlang;
    geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {

            returnlatlang = results[0].geometry.location;
            console.log(returnlatlang); // this is defined.
        } else {
            alert('Geocode was not successful for the following reason: ' + status);
        }
    });
    console.log(returnlatlang); // this is undefined.
    return returnlatlang;
}

在这种情况下，范围如何运作？

Answer 1

codeAddress在异步函数能够设置之前返回变量returnlatlong。

你可以使用Promise，一个基本的例子就是这样：

function codeAddress(address){
    return new Promise(function(resolve, reject){    
        geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            returnlatlang = results[0].geometry.location;
            resolve(returnlatlang); // this is defined.
        } else {
            reject('Geocode was not successful for the following reason: ' + status);
        }
    });
}
codeAddress('some address').then(function(){
   //the promise resolved
}, function(){
   //the promise rejected
});