global_local test

    <script type="text/javascript">
        var str = "global";
        function test() {
            alert(str); //undefined
            var str = "local";
        }
        test();
        alert(str); //global
    </script>

undefined
global

    <script type="text/javascript">
        var str = "global";
        function test() {
            alert(str); //global
        }
        test();
        alert(str); //global
    </script>

global
global