Basic JS file with a toggle

script.js

// get the button
var btnContent = document.getElementById("btn-content");
// add a click event
btnContent.addEventListener("click", toggleContent);

// get the content
var content = document.getElementById("content");
// hide by default
content.style.display = "none";

// when button is clicked, show/hide
function toggleContent() {
  var myContent = document.getElementById("content");
  if (myContent.style.display === "none") {
    myContent.style.display = "block";
  } else {
    myContent.style.display = "none";
  }
}