<
script 
type
="text/javascript">
        var 
a = "hello"
;
        b = "world"
;
        Test();
        function 
Test() {
            alert(a + " " 
+ b);
            var 
a = "welcome"
;
            b = "china"
;
            alert(a + " " 
+ b);
        }
        alert(a + " " 
+ b);
    script
>

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预编译后

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   <
script 
type
="text/javascript">
        var 
a = "hello"
;
        b = "world"
;
        
        function 
Test() {
            
            var 
a = "undefined"
;
?           alert(a + " " 
+ b);
            
a = "welcome"
;
            b = "china"
;
            alert(a + " " 
+ b);
        }
        Test();
       ?alert(a + " " 
+ b);
    script
>

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当我们写下：var i=1时，其实就是声明了一个window作用域的一个变量。

　　而当我们写下i=1时，是声明了一个window的属性。

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