css.js

if (typeof window !== 'undefined') {
  var waitSeconds = 100;

  var head = document.getElementsByTagName('head')[0];

  // get all link tags in the page
  var links = document.getElementsByTagName('link');
  var linkHrefs = [];
  for (var i = 0; i < links.length; i++) {
    linkHrefs.push(links[i].href);
  }

  var isWebkit = !!window.navigator.userAgent.match(/AppleWebKit\/([^ ;]*)/);
  var webkitLoadCheck = function(link, callback) {
    setTimeout(function() {
      for (var i = 0; i < document.styleSheets.length; i++) {
        var sheet = document.styleSheets[i];
        if (sheet.href == link.href)
          return callback();
      }
      webkitLoadCheck(link, callback);
    }, 10);
  };

  var noop = function() {};

  var loadCSS = function(url) {
    return new Promise(function(resolve, reject) {
      var timeout = setTimeout(function() {
        reject('Unable to load CSS');
      }, waitSeconds * 1000);
      var _callback = function(error) {
        clearTimeout(timeout);
        link.onload = link.onerror = noop;
        setTimeout(function() {
          if (error)
            reject(error);
          else
            resolve('');
        }, 7);
      };
      var link = document.createElement('link');
      link.type = 'text/css';
      link.rel = 'stylesheet';
      link.href = url;
      if (!isWebkit) {
        link.onload = function() {
          _callback();
        }
        link.onerror = function(event) {
          _callback(event.error);
        }
      } else {
        webkitLoadCheck(link, _callback);
      }
      head.appendChild(link);
    });
  };

  exports.fetch = function(load) {
    // dont reload styles loaded in the head
    for (var i = 0; i < linkHrefs.length; i++)
      if (load.address == linkHrefs[i])
        return '';
    return loadCSS(load.address);
  };
}
else {
  exports.fetch = function(load) {
    // individually mark loads as not built for buildCSS false
    if (this.buildCSS === false)
      load.metadata.build = false;
    // setting format = 'defined' means we're managing our own output
    load.metadata.format = 'defined';
    // don't load the CSS at all until build time
    return '';
  };
  exports.instantiate = function() {};
  exports.bundle = function(loads, opts) {
    var loader = this;
    if (loader.buildCSS === false)
      return '';
    return loader['import']('./css-builder', { name: module.id }).then(function(builder) {
      return builder.call(loader, loads, opts);
    });
  };
}