BigInt64Array

// 
const bigint64 = new BigInt64Array(2);
bigint64[0] = 42n;
console.log(bigint64[0]); // 42n
console.log(bigint64.length); // 2
console.log(bigint64.BYTES_PER_ELEMENT); // 8

// 
const x = new BigInt64Array([21n, 31n]);
console.log(x[1]); // 31n

//  TypedArray
const y = new BigInt64Array(x);
console.log(y[0]); // 21n

// ArrayBuffer
const buffer = new ArrayBuffer(64);
const z = new BigInt64Array(buffer, 8, 4);
console.log(z.byteOffset); // 8

// 
const iterable = (function* () {
  yield* [1n, 2n, 3n];
})();
const bigint64FromIterable = new BigInt64Array(iterable);
console.log(bigint64FromIterable);
// BigInt64Array [1n, 2n, 3n]