Chrome extension scan web page and highlight key words.

content.js

  // Thoroughly untested.

  let searchTerms = ['law', 'software', 'news', 'health'];

  let elems = document.querySelectorAll("h1, h2, h3, h4, h5, h6, li, p, a")
  for (let i = 0, total = elems.length; i < total; i++) {
    let element = elems[i];
    if (element && element.innerText) {
      let innerText = element.innerText;
      for (let j = 0; j < searchTerms.length; j++) {
        const reg = new RegExp(searchTerms[j], 'gi')
        const matches = innerText.toLowerCase().match(reg) || []
        if (matches.length) {
          for (let n = 0; n < matches.length; n++) {
            element.innerHTML = innerText.replace(reg, '<span style="color:red">' + searchTerms[j] + '</span>');
          }
        }
      }
    }
  }