Element.prototype.removeChildren = () => {
  while(this.firstChild) {
    this.removeChild(this.firstChild);
  }
}

// the main problem of this script is not working prototype method 'removeChildren';
// but all without a method works perfectly!


var footer = document.querySelector('#footer');

footer.removeChildren();

// it doesn't work unfortunately!

for (var i = 0; i < footer.childElementCount; i++) {
  footer.removeChild(footer.firstChild);
}

// it works without problems!