toString() & toLowerCase() & toUpperCase()

toString():把陣列轉成字串

const stringObj = new String('foo');
const newObj=stringObj.toString();
console.log(newObj)
//"foo"

toLowerCase():字符串轉換為英文小寫字母后的結果

const sentence = 'The quick brown fox jumps over the lazy dog.';

console.log(sentence.toLowerCase());
//the quick brown fox jumps over the lazy dog.

toUpperCase():字符串轉換為英文大寫字母后的結果

const sentences = 'The is apple.';
console.log(sentences.toUpperCase());
//"THE IS APPLE."