TypedArray.prototype.at()

const int8 = new Int8Array([0, 10, -10, 20, -30, 40, -50]);
let index = 1;
console.log(`An index of ${index} returns the item ${int8.at(index)}`);
// Expected output: "An index of 1 returns the item 10"
index = -2;
console.log(`An index of ${index} returns the item ${int8.at(index)}`);
// Expected output: "An index of -2 returns the item 40"

at(index)

const uint8 = new Uint8Array([1, 2, 4, 7, 11, 18]);
// 指定された配列の最後の項目を返す関数です。
function returnLast(arr) {
  return arr.at(-1);
}
const lastItem = returnLast(uint8);
console.log(lastItem); // 18

// Our typed array with values
const uint8 = new Uint8Array([1, 2, 4, 7, 11, 18]);
// Using length property
const lengthWay = uint8[uint8.length - 2];
console.log(lengthWay); // 11
// Using slice() method. Note an array is returned
const sliceWay = uint8.slice(-2, -1);
console.log(sliceWay[0]); // 11
// Using at() method
const atWay = uint8.at(-2);
console.log(atWay); // 11