<button>ALERT</button>
button {
  font-size: 2rem;
  padding: 0.4em 1em;
}

body {
  display: grid;
  place-items: center;
  min-height: 100dvh;
}
const button = document.querySelector("button")
button.addEventListener("click", () => {
  alert('안녕하세요! 👋')
})

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External JavaScript

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