Get the number of elements in the current page

tag_class_count.js

console.log(
  [...document.querySelectorAll("*")]
    .map(el => el.nodeName)
    .sort()
    .filter((item, index, arr) => arr[index - 1] !== item).length
);

var s = new Set();
[...document.querySelectorAll("*")].forEach(el => s.add(el.nodeName));
console.log(s.size);