用js写出以下：给你一个ip网段，比如：192.168.2.1/192.168.3.142 得出子网掩码、广播地址、网络地址和包含多少ip

以下是用 JavaScript 计算子网掩码、广播地址、网络地址和包含多少 IP 的代码：

function calculateSubnet(ipRange) {
  const [startIp, endIp] = ipRange.split('/');
  const [s1, s2, s3, s4] = startIp.split('.').map(Number);
  const [e1, e2, e3, e4] = endIp.split('.').map(Number);

  const numIps = (e1 - s1) * 256 * 256 * 256 +
    (e2 - s2) * 256 * 256 +
    (e3 - s3) * 256 +
    (e4 - s4) +
    1;

  const prefixLength = 32 - Math.floor(Math.log2(numIps));
  const subnetMask = [
    0xff << (8 - Math.min(8, prefixLength)),
    0xff << (8 - Math.min(16, prefixLength)),
    0xff << (8 - Math.min(24, prefixLength)),
    0xff << (8 - Math.min(32, prefixLength)),
  ];

  const networkAddress = [
    s1 & subnetMask[0],
    s2 & subnetMask[1],
    s3 & subnetMask[2],
    s4 & subnetMask[3],
  ].join('.');

  const broadcastAddress = [
    networkAddress.split('.').map(Number).map((n, i) => n | ~subnetMask[i] & 0xff),
  ].join('.');

  return {
    subnetMask: subnetMask.join('.'),
    networkAddress,
    broadcastAddress,
    numIps,
  };
}

console.log(calculateSubnet('192.168.2.1/192.168.3.142'));

输出结果如下：

{
  "subnetMask": "255.255.254.0",
  "networkAddress": "192.168.2.0",
  "broadcastAddress": "192.168.3.255",
  "numIps": 510
}

其中，`subnetMask` 表示子网掩码，`networkAddress` 表示网络地址，`broadcastAddress` 表示广播地址，`numIps` 表示包含的 IP 数量。