template/src/transforms/meta.js

import favicon from '../assets/distill-favicon.base64';

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}" >\n`);
  }

  appendHead(`
    <meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1">
    <link rel="icon" type="image/png" href="data:image/png;base64,${favicon}">
    <link href="/rss.xml" rel="alternate" type="application/rss+xml" title="Articles from Distill">
    <link rel="canonical" href="${data.url}">
    <title>${data.title}</title>
  `);

  appendHead(`
    <!--  https://schema.org/Article -->
    <meta property="article:published" itemprop="datePublished" content="${data.publishedYear}-${data.publishedMonthPadded}-${data.publishedDayPadded}" />
    <meta property="article:modified" itemprop="dateModified" content="${data.updatedDate}" />
  `);
  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.jpg"/>
    <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.jpg">
    <meta name="twitter:image:width" content="560">
    <meta name="twitter:image:height" content="295">
  `);

  // if this is a proprer article, generate Google Scholar meta data
  if (data.doiSuffix){
    appendHead(`
      <!--  https://scholar.google.com/intl/en/scholar/inclusion.html#indexing -->\n`);

    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.publishedDate){
      meta('citation_publication_date', `${data.publishedYear}/${data.publishedMonthPadded}/${data.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 => {
        let d = data.bibliography[key];
        if(!d) {
          console.warn('No bibliography data fround for ' + key);
        } else {
          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;
}