[英]Explanation of the use of async defer for the Google Maps API
I'm trying to understand the loading of the <script>
elements in the code snippet at https://developers.google.com/maps/documentation/javascript/tutorial :我试图了解https://developers.google.com/maps/documentation/javascript/tutorial代码片段中
<script>
元素的加载:
<!DOCTYPE html>
<html>
<head>
<title>Simple Map</title>
<meta name="viewport" content="initial-scale=1.0">
<meta charset="utf-8">
<style>
/* Always set the map height explicitly to define the size of the div
* element that contains the map. */
#map {
height: 100%;
}
/* Optional: Makes the sample page fill the window. */
html, body {
height: 100%;
margin: 0;
padding: 0;
}
</style>
</head>
<body>
<div id="map"></div>
<script>
var map;
function initMap() {
map = new google.maps.Map(document.getElementById('map'), {
center: {lat: -34.397, lng: 150.644},
zoom: 8
});
}
</script>
<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap"
async defer></script>
</body>
</html>
Presumably, the google.maps.Map
object is defined in the latter script
.据推测,
google.maps.Map
对象是在后一个script
定义的。 However, that script has the async defer
attributes, which according to https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script means that it will be executed asynchronously and after the document has been parsed.但是,该脚本具有
async defer
属性,根据https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script意味着它将在文档被解析后异步执行. But since this comes after the first script
, how can the first script
instantiate a Map
before the definition has been loaded?但由于这是以后的第一个
script
,如何能第一script
实例化一个Map
的定义已经加载之前?
要将 Charlie 的评论转换为答案,Google Maps API src
末尾的&callback=initMap
确保在 Google Maps 加载完成后调用initMap
函数。
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