document.body.ƒ('ul li:last-child').innerText = "I'M THE NEW GUY!"; That code won't work in standards-compliant browsers. You should either use .textContent =

document.body.ƒ('ul li:last-child').innerText = "I'M THE NEW GUY!"; That code won't work in standards-compliant browsers. You should either use .textContent = "..." or .appendChild(document.createTextNode("...")) or .firstChild.wholeText = "..." if there's already a text node child. The real issue though is that unlike jQuery, ƒu.js won't work in popular versions of IE.