明确分配后在Javascript中未定义变量？

Question

For some reason my "initialLocation" variable is undefined when I make an alert on it, even though I explicitly assign it in the callback function for getCurrentPosition. Variable "initialLocation" is declared globally btw.

Maybe I'm not understanding this concept of closures?

var initialLocation;

if (navigator.geolocation) {
    geoLocationError = true;
    navigator.geolocation.getCurrentPosition(function(position) {
        initialLocation = new google.maps.LatLng(position.coords.latitude, position.coords.longitude);
        getFood();
        }, geoError);
    alert(initialLocation);
} else {
    geoLocationError = false;
    noGeolocation(geoLocationError);
}

Answer 1

navigator.geolocation.getCurrentPosition is asynchronous, so your alert is firing before initialLocation is set. You should place your alert inside the callback, just after you set initialLocation .