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来源：3-16 编程练习

__Promise

2021-05-24 15:20:48

<!DOCTYPE html>
<html>

<head lang="en">
    <meta charset="UTF-8">
    <title>toUpperCase和toLowerCase</title>
</head>

<body>
    <script>
        var str = "Never deter till tomorrow that which you can do today";
        var index = str.indexOf('tomorrow'); //补充代码
        var strNew = str.substr(index, 8); //补充代码
        var upperStr = strNew.toUpperCase(); //补充代码
        document.write(str.substring(0,index) + upperStr + str.substring(index+8));
    </script>
</body>

</html>