when to disconnect and when to end a pg client or pool

My stack is node, express and the pg module. I really try to understand by the documentation and some outdated tutorials. I dont know when and how to disconnect and to end a client.

For some routes I decided to use a pool. This is my code

const pool = new pg.Pool({
  user: 'pooluser',host: 'localhost',database: 'mydb',password: 'pooluser',port: 5432});

pool.on('error', (err, client) => {
  console.log('error ', err);  process.exit(-1);
});

app.get('/', (req, res)=>{
  pool.connect()
    .then(client => {
      return client.query('select ....')
            .then(resolved => {
              client.release();
              console.log(resolved.rows);
            })
            .catch(e => { 
              client.release();
              console.log('error', e);
            })
      pool.end();
    })
});

In the routes of the CMS, I use client instead of pool that has different db privileges than the pool.

const client = new pg.Client({
  user: 'clientuser',host: 'localhost',database: 'mydb',password: 'clientuser',port: 5432});    
client.connect();

const signup = (user) => {
  return new Promise((resolved, rejeted)=>{
    getUser(user.email)
    .then(getUserRes => {
      if (!getUserRes) {
        return resolved(false);
      }            
            client.query('insert into user(username, password) values ($1,$2)',[user.username,user.password])
              .then(queryRes => {
                client.end();
                resolved(true);
              })
              .catch(queryError => {
                client.end();
                rejeted('username already used');
              });
    })
    .catch(getUserError => {
      return rejeted('error');
    });
  }) 
};

const getUser = (username) => {
  return new Promise((resolved, rejeted)=>{
    client.query('select username from user WHERE username= $1',[username])
      .then(res => {
        client.end();
        if (res.rows.length == 0) {
          return resolved(true);
        }
        resolved(false);
      })
      .catch(e => {
        client.end();
        console.error('error ', e);
      });
  })
}

In this case if I get a username already used and try to re-post with another username, the query of the getUser never starts and the page hangs. If I remove the client.end(); from both functions, it will work.

I am confused, so please advice on how and when to disconnect and to completely end a pool or a client. Any hint or explanation or tutorial will be appreciated.

Thank you

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