code: function canonical() {
    var tags = document.getElementsByTagName('link');
    // eslint-disable-next-line no-cond-assign
    for (var i = 0, tag; tag = tags[i]; i++) {
      if (tag.getAttribute('rel') === 'canonical') {
        return tag.getAttribute('href');
      }
    }
  }
docs: Get the current page's canonical URL.
  
  @return {string|undefined}