我正在制作一个网络应用程序，让人们可以在谷歌地图上看到公交车的位置。我在JavaScript中的全局变量方面遇到了一些问题。window.variable对我不起作用，在所有函数之外定义变量也不起作用。这是我完整的客户端代码：
<!DOCTYPE html>
<html>
<head>
<title>Geolocation</title>
<meta name="viewport" content="initial-scale=1.0, user-scalable=no">
<meta charset="utf-8">
<style>
html, body, #map-canvas {
height: 100%;
margin: 0px;
padding: 0px
}
</style>
<script src="https://maps.googleapis.com/maps/api/js?v=3.exp"></script>
<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
<script>
// Note: This example requires that you consent to location sharing when
// prompted by your browser. If you see a blank space instead of the map, this
// is probably because you have denied permission for location sharing.
var old = [];
function getLocation()
{
$.get( "http://54.86.161.214/EC_bus_app/get_location.php", function( data ) {
old=[];
var buses = data;
var number_of_buses = buses.slice(0,1);
buses = buses.slice(2);
buses = buses.slice(0,-1);
var bus_coordinates_and_numbers = buses.split(/[ ]+/);
var length_of_array = bus_coordinates_and_numbers.length;
// Turn a single dimensional array into a multi-dimensional array
for (var index = 0; index < bus_coordinates_and_numbers.length; index+= 3)
old.push( bus_coordinates_and_numbers.slice(index, index + 3) );
console.log(old);
//initialize(old);
});
}
setInterval(getLocation, 10000);
var map;
function initialize() {
var mapOptions = {
zoom: 18
};
map = new google.maps.Map(document.getElementById('map-canvas'),
mapOptions);
var image = "icon_97.png";
for (i=0;i<old.length; i = i + 1){
var x = old[i][0];
var y = old[i][1];
var myLatlng = new google.maps.LatLng(x,y);
var busMarker = new google.maps.Marker({
position: myLatlng,
map: map,
icon: image,
title: old[i][2]
});
}
// Try HTML5 geolocation
if(navigator.geolocation) {
navigator.geolocation.getCurrentPosition(function(position) {
var pos = new google.maps.LatLng(position.coords.latitude,
position.coords.longitude);
var infowindow = new google.maps.InfoWindow({
map: map,
position: pos,
content: 'Your location'
});
map.setCenter(pos);
}, function() {
handleNoGeolocation(true);
});
} else {
// Browser doesn't support Geolocation
handleNoGeolocation(false);
}
}
function handleNoGeolocation(errorFlag) {
if (errorFlag) {
var content = 'Error: The Geolocation service failed.';
} else {
var content = 'Error: Your browser doesn't support geolocation.';
}
var options = {
map: map,
position: new google.maps.LatLng(60, 105),
content: content
};
var infowindow = new google.maps.InfoWindow(options);
map.setCenter(options.position);
}
google.maps.event.addDomListener(window, 'load', initialize);
</script>
</head>
<body>
<div id="map-canvas"></div>
</body>
</html>
所讨论的变量是old。我可以使用initialize(old);将它从get location函数中传递给initialize函数。但是，正如您所看到的，我使用的是计时器，initialize(old);会导致整个地图一次又一次地重新加载，而我只希望位置标记一次又一遍地加载。
通过在initialize()中移动getLocation()解决了问题。但@geocodezip在评论中所说的话也完全回答了我的问题。
问题不在于全局变量。它具有异步功能。您需要初始化映射，然后请求数据（异步请求），在映射上制作标记，然后定期更新它们。