const values = new Array<number>(3);
values[0] = 1;
values[2] = 3;
const boxed: unknown = values;
const checked = boxed as number[];
console.log(checked.length, 0 in checked, 1 in checked, 2 in checked, checked.join(","));
console.log(Object.keys(boxed as object).join(","), JSON.stringify(boxed));
checked[1] = 2;
console.log(values.join(","), (boxed as number[]).join(","));
checked.length = 5;
console.log(3 in values, Object.keys(boxed as object).join(","));
const copied = structuredClone(boxed) as number[];
console.log(copied.length, 3 in copied, copied.join(","));