功能
將陣列轉變為字串，並且選擇連結符。
範例
const arr=["moko", "dog", "swimming"];
const str1=arr.join(",");//用逗號連接
console.log(str1);//"moko,dog,swimming"
const str2=arr.join("");//不要連結
console.log(str2);//"mokodogswimming"將陣列轉變為字串，並且選擇連結符。
const arr=["moko", "dog", "swimming"];
const str1=arr.join(",");//用逗號連接
console.log(str1);//"moko,dog,swimming"
const str2=arr.join("");//不要連結
console.log(str2);//"mokodogswimming"