<script>
let str = "Hello World!";
// 將字串的字符全部轉換為小寫字符
function lowerCase(str) {
let arr = str.split("");
let newStr = "";
//通過for回圈遍歷陣列
for (let i = 0; i < arr.length; i++) {
if (arr[i] >= 'A' && arr[i] <= 'Z')
newStr += arr[i].toLowerCase();
else
newStr += arr[i];
}
return newStr;
}
// 將字串的字符全部轉換為大寫字符
function upperCase(str) {
let arr = str.split("");
let newStr = "";
// 通過陣列的forEach方法來遍歷陣列
arr.forEach(function (value) {
if (value >= 'a' && value <= 'z')
newStr += value.toUpperCase();
else
newStr += value;
});
return newStr;
}
let res1 = lowerCase(str);
let res2 = upperCase(str);
console.log(res1);
console.log(res2);
</script>

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