long poll pratice

long-poll.js

const p = require('polka')();
const debounce = require('lodash/debounce');

p.get('/', (req, res) => {
    res.end('hello world')
})

const maxConnections = 10*10000;
const todos = ['hello'];
const users = Object.create(null);


p.post('/long-poll/:UserID', (req, res) => {
    const { UserID } = req.params;
    if (!UserID) return res.end('error');
    
    if (!users[UserID]) {
      users[UserID] = Object.create(null);
      res.end(JSON.stringify(todos));
      count++;
      if (count >= maxConnections) {
          checkExpiredConnection(Object.keys(users), 5000);
      }
    } else {
      users[UserID].sub && users[UserID].sub('Warn The Old One has a new client, and stop pooling');
      users[UserID].time = +new Date();
      users[UserID].sub = function(todos) {
        res.end(JSON.stringify(todos));
      }
    }
})

// delete lost connections;
const checkExpiredConnection = debounce(function (uks, expired, cb) {
    uks.forEach(k => {
        const {time, sub} = users[k];
        if (+new Date() - time >= expired) { // if ten seconds long，end；
            sub && sub('');
            delete users[k];
            count--;
        }
        sub && sub(todo);
    })
    cb && cb();
}, 200);

// loop check
function loopCheckExpiredConnection() {
    setTimeout(() => {
        checkExpiredConnection(Object.keys(users), 10000, loopCheckExpiredConnection);
    }, 10000)
}

// debounce process emit new todos
const emitNewTodo = debounce(function(todo, PrevID) {
    Object.keys(users).forEach(k => {
        const {sub} = users[k];
        let goon = null;
        for (let i = 0; i<=todos.length; i++) {
            if (todos[i].ID === PrevID) {
                goon = [];
            }
            if (goon) {
                goon.push(todos[i])
            }
        }
        sub && sub(goon);
    });
}, 200);

p.get('/new/todo/:todo', (req, res) => {
    const {todo, PrevID} = req.params;
    todos.push(todo);
    res.end('ok');
    emitNewTodo(todo, PrevID);
})

p.get('/cache', (req, res) => {
    res.end(JSON.stringify({todos: todos, users: users,}))
})

p.listen(3000).then(() => {
    loopCheckExpiredConnection();
    console.log('> Running on localhost:3000');
})