String Methods
不會更動原始字串
（回傳新字串、索引值、某個值、或產生新的陣列）
String split()：將字串拆分為陣列，並返回一個新陣列。
split(separator);
split(separator, limit);const str = "The quick brown fox jumps over the lazy dog.";
const subWords = str.split(" ");
console.log(subWords);
// Expected output: Array ["The", "quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog."]
const words = str.split(" ");
console.log(words[3]);
// Expected output: "fox"
const chars = str.split("");
console.log(chars[8]);
// Expected output: "k"
const strCopy = str.split();
console.log(strCopy);
// Expected output: Array ["The quick brown fox jumps over the lazy dog."]