[ruslan_mart]

function mouseEnter() {
    var span = document.createElement('span');
    span.innerHTML = 'В div перед p';
    this.insertBefore(span, this.firstChild);
}
 
function mouseLeave() {
    this.removeChild(this.firstChild);
}


var div = document.querySelectorAll('div[data-add-back-btn]');

for(var i = 0; i < div.length; i++) {
   div[i].addEventListener('mouseenter', mouseEnter);
   div[i].addEventListener('mouseleave', mouseLeave);
}