bionicReading.js

// Reference: https://github.com/tobyxdd/bread/blob/master/bread.js

function processWord(word, node) {
  const len = word.length;
  const boldLen = Math.ceil(len * 0.45); // might need an exception for 1 letter words

  const boldText = word.substring(0, boldLen);
  const normText = word.substring(boldLen);

  const span = document.createElement("span");

  span.style.fontWeight = "bolder";
  span.appendChild(document.createTextNode(boldText));

  node.parentNode.insertBefore(span, node);
  node.parentNode.insertBefore(document.createTextNode(`${normText} `), node);
}

function processNode(node) {
  const text = node.textContent;
  const words = text.split(" ");

  words.forEach((word) => processWord(word, node));

  node.remove();
}

// customize for your content
const textNodes = document.querySelectorAll(
  "#contentPanel > div > div.EOs2MW > div > div.bWSNNT > div._14BzLL span"
);

textNodes.forEach(processNode);