template/components/meta.js

export default function(dom, data) {
  let head = dom.querySelector("head");
  let appendHead = html => appendHtml(head, html);

  function meta(name, content) {
    if (content)
      appendHead(`<meta name="${name}" content="${content}" >`);
  }

  appendHead(`
    <meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1">
    <link rel="icon" type="image/png" href="/favicon.png">
    <link href="/rss.xml" rel="alternate" type="application/rss+xml" title="Articles from Distill">
    <link rel="canonical" href="${data.url}">
    <title>${data.title}</title>
  `);

  appendHead(`
    <!--  https://schema.org/Article -->
    <meta property="article:published" itemprop="datePublished" content="${data.published}" />
    <meta property="article:modified" itemprop="dateModified" content="${data.updated}" />
  `);
  data.authors.forEach((a) => {
    appendHtml(head, `
      <meta property="article:author" content="${a.firstName} ${a.lastName}" />`)
  });

  appendHead(`
    <!--  https://developers.facebook.com/docs/sharing/webmasters#markup -->
    <meta property="og:type" content="article"/>
    <meta property="og:title" content="${data.title}"/>
    <meta property="og:description" content="${data.description}">
    <meta property="og:url" content="${data.url}"/>
    <meta property="og:image" content="${data.url}/thumbnail.png"/>
    <meta property="og:locale" content="en_US" />
    <meta property="og:site_name" content="Distill" />
  `);

  appendHead(`
    <!--  https://dev.twitter.com/cards/types/summary -->
    <meta name="twitter:card" content="summary_large_image">
    <meta name="twitter:title" content="${data.title}">
    <meta name="twitter:description" content="${data.description}">
    <meta name="twitter:url" content="${data.url}">
    <meta name="twitter:image" content="${data.url}/thumbnail.png">
    <meta name="twitter:image:width" content="560">
    <meta name="twitter:image:height" content="295">
  `);

  appendHead(`
    <!--  https://scholar.google.com/intl/en/scholar/inclusion.html#indexing -->
  `);

  meta("citation_title", data.title);
  meta("citation_fulltext_html_url", data.url);
  meta("citation_volume", data.volume);
  meta("citation_issue", data.issue);
  meta("citation_firstpage", data.doiSuffix? `e${data.doiSuffix}` : undefined);
  meta("citation_doi", data.doi);

  let journal = data.journal || {};
  meta("citation_journal_title", journal.name);
  meta("citation_journal_abbrev", journal.nameAbbrev);
  meta("citation_issn", journal.issn);
  meta("citation_publisher", journal.publisher);

  if (data.published){
    let zeroPad = (n) => { return n < 10 ? "0" + n : n; };
    let publishedYear = data.published.getFullYear();
    let publishedMonthPadded = zeroPad(data.published.getMonth() + 1);
    let publishedDayPadded = zeroPad(data.published.getDate());
    meta("citation_publication_date", `${publishedYear}/${publishedMonthPadded}/${publishedDayPadded}`);
  }

  (data.authors || []).forEach((a) => {
      meta("citation_author", `${a.lastName}, ${a.firstName}`);
      meta("citation_author_institution", a.affiliation);
  });

  if (data.citations) {
    data.citations.forEach(key =>
        meta("citation_reference", citation_meta_content(data.bibliography[key]) )
      );
  }
}


function appendHtml(el, html) {
  el.innerHTML += html;
}

function citation_meta_content(ref){
  var content = `citation_title=${ref.title};`;
  ref.author.split(" and ").forEach(author => {
    content += `citation_author=${author.trim()};`;
  });
  if ("journal" in ref){
    content += `citation_journal_title=${ref.journal};`;
  }
  if ("volume" in ref) {
      content += `citation_volume=${ref.volume};`;
  }
  if ("issue" in ref || "number" in ref){
      content += `citation_number=${ref.issue || ref.number};`;
  }
  /*content += `citation_first_page=${};`;
  content += `citation_publication_date=${};`;*/
  return content;
}