怎样写才能使结果输出为 b

<html>
<head>
</head>
<body ><script>
var newchar='a'.charCodeAt(0);
newchar+=1;
alert(String.fromCharCode(newchar));
</script>
多谢！  
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c=String.fromCharCode(65)  
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str.charCodeAt(x)，表示将字符串str中的第x个字符转变成ASCII值  
       求ASCII转字符：javascript用String.fromCharCode(x);vbscript用chr(x)或chrw(x)  
       求字符转ASCII：javascript用??;vbscript用asc('字符')  
</body>
</html>