The fastest way to escape HTML strings known to me~~n~~, if you need to do so with JS and you are inside a browser.

fastest_escape_html.js

// Can you make this faster? Ping me.

const escapeHtml = (function () {
  const serializer = new XMLSerializer ();
  const attr = document.createAttribute ( 'attr' );
  const re = /[&<>"]/;
  return function escapeHtml ( str ) {
    if ( !re.test ( str ) ) return str;
    attr.value = str;
    return serializer.serializeToString ( attr );
  }
})()