const el = document.body.appendChild(

  document.createElement('div')

);

el.innerHTML = `

<button>one</button>

<button>two</button>

<button>three</button>

`;

document.addEventListener('click', e => {

  e.target.focus();

});

const origFocus = HTMLElement.prototype.focus

HTMLElement.prototype.focus = function() {

  console.log(this.outerHTML, 'focus was called');

  origFocus.call(this);

};

el.firstElementChild.focus();