TypedArray.prototype.copyWithin()

const uint8 = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8]);

// 
uint8.copyWithin(3, 1, 3);

console.log(uint8);
// : Uint8Array [1, 2, 3, 2, 3, 6, 7, 8]

copyWithin(target, start)
copyWithin(target, start, end)

const buffer = new ArrayBuffer(8);
const uint8 = new Uint8Array(buffer);
uint8.set([1, 2, 3]);
console.log(uint8); // Uint8Array [ 1, 2, 3, 0, 0, 0, 0, 0 ]
uint8.copyWithin(3, 0, 3);
console.log(uint8); // Uint8Array [ 1, 2, 3, 1, 2, 3, 0, 0 ]