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我试图了解https://developers.google.com/maps/documentation/javascript/tutorial<script>代码片段中元素的加载：

<!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>

据推测，google.maps.Map对象是在后者中定义的script。但是，该脚本具有async defer属性，根据https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script ，这意味着它将在文档被解析后异步执行。但是由于这是在 first 之后， firstscript如何在定义加载之前script实例化 a ？Map

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1 回答 1

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要将 Charlie 的评论转换为答案， Google Maps API&callback=initMap末尾的src确保initMap在 Google Maps 完成加载后调用该函数。

于 2018-08-19T22:14:36.707 回答