Defined global variable in javascript becomes undefined again
<pre><code>&lt;!DOCTYPE html&gt;
&lt;html lang="en"&gt;
&lt;head&gt;&lt;meta charset="utf-8" /&gt;
    &lt;script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?sensor=false&amp;region=vi&amp;language=vi"&gt;    
    &lt;/script&gt;

    &lt;script type="text/javascript" src="jquery-1.7.1.min.js"&gt;&lt;/script&gt;
    &lt;script type="text/javascript"&gt;
        var map;
    &lt;/script&gt;
    &lt;style type="text/css"&gt;
        html {
            height: 100%;
        }

        body {
            height: 100%;
            margin: 0;
            padding: 0;
        }
    &lt;/style&gt;
&lt;/head&gt;

&lt;body onload="initialize()"&gt;
    &lt;div id="map_canvas" style="width: 100%; height: 100%"&gt;&lt;/div&gt;

    &lt;script type="text/javascript"&gt;
        function initialize() {
            var mapOptions = {
                center: new google.maps.LatLng(10.79, 826.694),
                zoom: 13,
                mapTypeId: google.maps.MapTypeId.ROADMAP
            };
            map = new google.maps.Map(document.getElementById("map_canvas"),
                mapOptions);
        }
    &lt;/script&gt;    

    &lt;script&gt;            
        alert(map);
    &lt;/script&gt;

&lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>A couple of my functions need to use the <code>map</code> variable, however, I keep receiving alerts that complain <code>map</code> variable is unidentified.
How can I make browser remember that map was defined on <code>map = new google.maps.Map(document.getElementById("map_canvas"),
                    mapOptions);</code>
Thank you</p>
