webextensions/src/scripts/contentscript.js

import ext from "./utils/ext";
import storage from "./utils/storage";

var extractTags = () => {
  var url = document.location.href;
  if (!url || !url.match(/^http/)) {
    console.error("Invalid URL : " + url);
    return;
  }

  var data = {
    title: "",
    description: "",
    image: "",
    url: url
  };

  var ogTitle = document.querySelector("meta[property='og:title']");
  if (ogTitle) {
    data.title = ogTitle.getAttribute("content");
  } else {
    data.title = document.title;
  }

  var descriptionTag =
    document.querySelector("meta[property='og:description']") ||
    document.querySelector("meta[name='description']");
  if (descriptionTag) {
    data.description = descriptionTag.getAttribute("content");
  }

  var imgTag =
    document.querySelector("meta[property='og:image']") ||
    document.querySelector("meta[property='twitter-image']");
  if (imgTag) {
    data.image = imgTag.getAttribute("content");
  } else {
    imgTag =
      document.querySelector("link[rel=icon]") ||
      document.querySelector("link[rel=apple-touch-icon]");
    if (imgTag) {
      data.image = imgTag.getAttribute("href");
    }
  }

  return data;
};

function onRequest(request, sender, sendResponse) {
  if (request.action === "process-page") {
    sendResponse(extractTags());
  }
}

ext.runtime.onMessage.addListener(onRequest);