(1) UPDATE - textContent, classList.add

const oneDiv = document.createElement('div')

console.log(oneDiv) // <div></div>
oneDiv.textContent = 'dev';
console.log(oneDiv) // <div>dev</div>

oneDiv.classList.add('tweet')
console.log(oneDiv) // <div class="tweet">dev</div>

const container = document.querySelector('#container')
container.append(oneDiv)

const oneDiv = document.createElement('div') // div 엘리먼트 생성
oneDiv.textContent = 'dev' // div 엘리먼트에 dev 입력

oneDiv.classList.add('tweet') // class 추가 한다.

const container = document.querySelector('#container') // 컨테이너 호출

container.append(oneDiv) 컨테이너의 자식요소로 추가한다.

oneDiv
<div class="tweet">dev</div>

(2)DELETE - remove, removeChild

const container = document.querySelector('#container')
const tweetDiv = document.createElement('div')
container.append(tweetDiv)
tweetDiv.remove() // 이렇게 append 했던 엘리먼트를 삭제할 수 있다.

const container = document.querySelector('#container');
while (container.firstChild) {
  container.removeChild(container.firstChild);
}

const container = document.querySelector('#container');
while (container.children.length > 1) {
  container.removeChild(container.lastChild);
}

const tweets = document.querySelectorAll('.tweet')
tweets.forEach(function(tweet){
    tweet.remove();
})
// or
for (let tweet of tweets){
    tweet.remove()
}

(3)Further Study