function get_last_N_bits(number, N) {
let mask = (1 << N) - 1;
return number & mask;
}
const number = 441; // 00000001101-11001
const N = 5;
console.log(("0000000000000000" + number.toString(2)).substr(-16));
let lastNbits = get_last_N_bits(number, N);
console.log(("0000000000000000" + lastNbits .toString(2)).substr(-16));
/*
run:
0000000110111001
0000000000011001
*/