String.prototype.at()

const sentence = "The quick brown fox jumps over the lazy dog.";
let index = 5;
console.log(`An index of ${index} returns the character ${sentence.at(index)}`);
// 予想される結果: "An index of 5 returns the character u"
index = -4;
console.log(`An index of ${index} returns the character ${sentence.at(index)}`);
// 予想される結果: "An index of -4 returns the character d"

at(index)

// 指定された文字列の最後の文字を返す関数
function returnLast(str) {
  return str.at(-1);
}
let invoiceRef = "my-invoice01";
console.log(returnLast(invoiceRef)); // '1'
invoiceRef = "my-invoice02";
console.log(returnLast(invoiceRef)); // '2'

const myString = "Every green bus drives fast.";
// length プロパティと charAt() メソッドの使用
const lengthWay = myString.charAt(myString.length - 2);
console.log(lengthWay); // 't'
// slice() メソッドの使用
const sliceWay = myString.slice(-2, -1);
console.log(sliceWay); // 't'
// at() メソッドの使用
const atWay = myString.at(-2);
console.log(atWay); // 't'