Simple functions for performing netmask checks on an IP.

netmask.js

function IPBInt(ip) {
	const iparr = ip.split(".");
	let bip = 0n;
	for(let i=0;i<iparr.length;i++) {
		bip = bip << 8n;
		bip += BigInt(iparr[i]);
	}
	return bip;
}

function maskMatch(ip,dest,mask) {
	ip = IPBInt(ip);
	dest = IPBInt(dest);
	mask = IPBInt(mask);
	return ((~(ip^dest))&mask)===mask;
}