HTML Demo

index.css

h1 { color: green; cursor: pointer; font-family: monospace;}
h1:hover { text-decoration: underline; }

index.html

<h1>Hello RunJS(from <a href="https://gist.github.com/bluishoul/d390f0981a8a1100bdc2d7f6a3a58935" target="_blank">Gist</a>)!!!</h1>
<script>
  const sayHello = () => { console.log("Hello RunJS!"); };
  sayHello();
</script>

index.js

document.querySelector("h1").addEventListener("click", () => {
  console.log("Hello World!");
});