CODE EXAMPLE FOR JAVASCRIPT

change style selected text js

function changeFont(font) {
  var sel = window.getSelection(); // Gets selection
  if (sel.rangeCount) {
    // Creates a new element, and insert the selected text with the chosen font inside
    var e = document.createElement('span');
    e.style = 'font-family:' + font.value + ';'; 
    e.innerHTML = sel.toString();

    // https://developer.mozilla.org/en-US/docs/Web/API/Selection/getRangeAt
    var range = sel.getRangeAt(0);
    range.deleteContents(); // Deletes selected text…
    range.insertNode(e); // … and inserts the new element at its place
  }
}