Role Members (JSON)

const fs = require("fs")
let data = JSON.parse(fs.readFileSync("./data.json", "utf8"));
var prefix = 'yourprefix'
client.on("message", async message => {
  if(message.content.startsWith(prefix + "set")) {
  var args = message.content.split(" ").slice(1)
  if(!args[0] || !args[1] ) return message.channel.send("> **Use:** " + prefix + "set [role-id]  [voice-channel-id] ");
    let ro = message.guild.roles.get(args[0]);
    if (!ro) return message.channel.send("> **I can't find this channel!**")
var ch = client.channels.get(args[1])
    if (!ch) return message.channel.send("> **I can't find this role!**")
     data = {role:args[0], channel:args[1]}
    fs.writeFile('./data.json', JSON.stringify(data, null, 4), function(err) {if(err) console.log(err)});
     message.channel.send("> **Done..**:white_check_mark:")
  }
})
client.on('guildMemberUpdate', member => {
    if(!data.role) return console.log("Error .")
  var role = member.guild.members.filter (m => m.roles.get(data.role))
  member.guild.channels.get(data.channel).setName(`Members: [${role.size}]`)
 });