This function illustrates how to programmatically select all text inside any HTML element

click.to.select.text.js

function selectText(element) {
  if (element.nodeName === 'INPUT' || element.nodeName === 'TEXTAREA') {
    element.select();
    return;
  }
  
  var rangeObj, selection;
  if (document.createRange) { // IE >=9 and all other browsers
    rangeObj = document.createRange();
    rangeObj.selectNodeContents(element);
    selection = window.getSelection();
    selection.removeAllRanges();
    selection.addRange(rangeObj);
  } else if (document.body.createTextRange) { // IE <9
    rangeObj = document.body.createTextRange();
    rangeObj.moveToElementText(element);
    rangeObj.select();
  }
}

// from https://www.thewebflash.com/select-or-deselect-text-inside-an-element-using-js/