generatePreview.js

const request = require("sync-request");
const cheerio = require("cheerio");
const urlUtil = require("url");

// finds title in the DOM passed
const findTitleInDom = $dom => {
  return (
    $dom("meta[property='og:title']").attr("content") ||
    $dom("title").text() ||
    $dom("meta[name=title]").attr("content")
  );
};

// finds description in the DOM passed
const findDescriptionInDom = $dom => {
  return (
    $dom("meta[property='og:description']").attr("content") ||
    $dom("meta[name=description]").attr("content") ||
    $dom("div .description").text()
  );
};

// finds image in the DOM passed
const findImageInDom = $dom => {
  var imageSrc =
    $dom("meta[property='og:image']").attr("content") ||
    $dom("meta[itemprop=image]").attr("content") ||
    $dom("link[rel=image_src]").attr("content") ||
    $dom("img").attr("src");
  return imageSrc;
};

// const validateUrl = (value) => (/(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9:%._\+~#=^@]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9:%_\+.~#?&//=^@]*)/g).test(value)

let cache = {};

const generatePreview = url => {
  // fetches the provided url
  if (cache.hasOwnProperty(url)) return cache[url];

  try {
    body = request("GET", url, { timeout: 10000 }).getBody();
    const $dom = cheerio.load(body);
    const descr = findDescriptionInDom($dom);
    let title = findTitleInDom($dom);
    title = title ? title : url;

    let img = findImageInDom($dom);
    img = img ? urlUtil.resolve(new urlUtil.URL(url).href, img) : "";

    const html = `<div class="linkPreviewContainer">
                <a href="${url}" data-href="${url}" title="${url}" rel="nofollow" target="_blank" class="linkPreviewText">
                    <strong>${title}</strong><br>
                    <em>${descr}</em>${url}</a>
                <a
                    href="${url}" class="linkPreviewImage" target="_blank" style="background-image: url(${img});"></a>
            </div>`;

    cache[url] = html;
    return html;
  } catch (e) {
    // if the fetch fails (no internet connection or dead link) return a plain link
    return `<a target="_blank" href="${url}">${url}</a>`;
  }
};

module.exports = generatePreview;