pluginVM.js

function PluginVM() {
  this.onInit = function() {
    const button = document.createElement("button"),
      div = document.createElement("div");

    button.innerHTML = "Executar plugin";

    button.addEventListener("click", PluginVM.makeChanges);

    button.className += "btn btn-danger";

    button.setAttribute("id", "buttonPluginVM");

    button.style.position = "fixed";
    button.style.zIndex = "2";
    button.style.bottom = "10px";
    button.style.fontFamily = "Arial";

    div.style.width = "100%";
    div.style.display = "flex";
    div.style.justifyContent = "center";

    document.body.appendChild(div);
    div.appendChild(button);
  };

  this.makeChanges = function() {
    var aux,
      temp,
      filterFunction,
      filteredTree,
      textNodes = [];

    filterFunction = function(node) {
      return (node.nodeType === 3 &&
        node.textContent.trim() !== "" &&
        node.parentNode.id != "buttonPluginVM") ||
        node.tagName == "IMG"
        ? NodeFilter.FILTER_ACCEPT
        : NodeFilter.FILTER_SKIP;
    };

    temp = /MSIE|Trident/.test(navigator.userAgent)
      ? filterFunction
      : {
          acceptNode: filterFunction
        };

    filteredTree = document.createTreeWalker(
      document.body,
      NodeFilter.SHOW_ALL,
      temp,
      false
    );

    while ((aux = filteredTree.nextNode())) textNodes[textNodes.length] = aux;

    for (var i = textNodes.length - 1; i >= 0; i--) {
      const element = textNodes[i];

      setFontSizeAndFamily(element.parentNode);

      if (element.tagName === "A") setHighlightsInLinks(element.parentNode);

      if (element.tagName == "IMG" && !element.getAttribute("alt"))
        setHighlightsInImages(element);
    }
  };

  function setFontSizeAndFamily(element) {
    element.style.setProperty(
      "font-size",
      parseFloat(getComputedStyle(element).fontSize) * 1.2 + "px"
    );
    element.style.setProperty("font-family", "Arial");
  }

  function setHighlightsInLinks(element) {
    element.style.setProperty("background-color", "#FFE599");
    element.style.setProperty("text-decoration", "underline");
    element.style.setProperty("font-style", "italic");
  }

  function setHighlightsInImages(element) {
    element.style.setProperty("border", "5px dotted red");
  }
}

var PluginVM = new PluginVM();

PluginVM.onInit();