chatroom.js

(function connect(){
    let socket = io.connect('http://localhost:3000')
    let username = document.querySelector('#username')
    let usernameBtn = document.querySelector('#usernameBtn')
    let curUsername = document.querySelector('.card-header')
    
    usernameBtn.addEventListener('click', e => {
        console.log(username.value)
        socket.emit('change_username', {username: username.value})
        curUsername.textContent = username.value
        username.value = ''
    })
})()