use promises for template's data in Express.js

promise-support-for-template.js

import _ from 'lodash';

function makeStatic(data) {
  return Promise.all(_.map(data, function map(v, k) {
    if (v instanceof Promise) {
      return v.then(x => x, () => null)
              .then(data => [k, data]);
    }

    return [k, v];
  })).then(function success(values) {
    return _.reduce(values, (x, y) => _.assign(x, { [y[0]]: y[1] }), {});
  });
}

/* ... */
app.use('/', function route(req, res) {
  /* ... */

  makeStatic(data).then(data => res.render('index', data));
});