JSFiddle - React, Tailwind, and code Playground

HTML

<button id="btn">인사</button>

JavaScript

var btnEle = document.getElementById('btn');

function outer() {
  var str1 = '안녕하세요';
  
  function inner() {
    alert(str1);
  }
  
  return inner()
}

btnEle.addEventListener('click', outer)