I took the following code from another question however it is not working for me....can anyone say why? how to get this part working?
Array.from(document.querySelectorAll('.watermarked')).forEach(function(el) {
      el.dataset.watermark = (el.dataset.watermark + ' ').repeat(300);
    });
I placed it in script tags
Array.from(document.querySelectorAll('.watermarked')).forEach(function(el) {
  el.dataset.watermark = (el.dataset.watermark + ' ').repeat(300);
});
.watermarked {
  position: relative;
  overflow: hidden;
}
.watermarked img {
  width: 100%;
}
.watermarked::before {
  position: absolute;
  top: -75%;
  left: -75%;
  display: block;
  width: 150%;
  height: 150%;
  transform: rotate(-45deg);
  content: attr(data-watermark);
  opacity: 0.7;
  line-height: 3em;
  letter-spacing: 2px;
  color: #fff;
}
<div class="watermarked" data-watermark="howbloggerz">
  <img src="http://www.w3schools.com/css/img_fjords.jpg">
</div>