Replace ® with superscript version

superscript.js

window.addEventListener('DOMContentLoaded', () => {
    const walk = document.createTreeWalker(
        document.body, 
        NodeFilter.SHOW_TEXT, 
        null, 
        false
    );

    const reg = /®/g;
    let node;

    // Use a list to avoid mutating the DOM while walking
    const nodesToReplace = [];
    while (node = walk.nextNode()) {
        if (node.parentElement.tagName !== 'SUP' && node.nodeValue.includes('®')) {
            nodesToReplace.push(node);
        }
    }

    nodesToReplace.forEach(textNode => {
        const parent = textNode.parentElement;
        const parts = textNode.nodeValue.split(reg);
        const fragment = document.createDocumentFragment();

        parts.forEach((part, i) => {
            fragment.appendChild(document.createTextNode(part));
            if (i < parts.length - 1) {
                const sup = document.createElement('sup');
                sup.textContent = '®';
                fragment.appendChild(sup);
            }
        });

        parent.replaceChild(fragment, textNode);
    });
});

Alternative version:

// Hell yeah treewalker!
document.createTreeWalker(document.body, NodeFilter.SHOW_TEXT).nextNode();

const walk = document.createTreeWalker(document.body, NodeFilter.SHOW_TEXT);
let n;
while (n = walk.nextNode()) {
  if (n.nodeValue.includes('®') && n.parentElement.tagName !== 'SUP') {
    n.replaceWith(...n.nodeValue.split(/(®)/g).map(t => 
      t === '®' ? Object.assign(document.createElement('sup'), {textContent: '®'}) : t
    ));
  }
}