BigUint64Array

// From a length
const biguint64 = new BigUint64Array(2);
biguint64[0] = 42n;
console.log(biguint64[0]); // 42n
console.log(biguint64.length); // 2
console.log(biguint64.BYTES_PER_ELEMENT); // 8

// From an array
const x = new BigUint64Array([21n, 31n]);
console.log(x[1]); // 31n

// From another TypedArray
const y = new BigUint64Array(x);
console.log(y[0]); // 21n

// From an ArrayBuffer
const buffer = new ArrayBuffer(64);
const z = new BigUint64Array(buffer, 8, 4);
console.log(z.byteOffset); // 8

// From an iterable
const iterable = (function* () {
  yield* [1n, 2n, 3n];
})();
const biguint64FromIterable = new BigUint64Array(iterable);
console.log(biguint64FromIterable);
// BigUint64Array [1n, 2n, 3n]