Native Nunjucks templating support for Koa v2

nunjucks.js

/*
USAGE:

import njk from './nunjucks';

// Templating - Must be used before any router
app.use(njk(path.join(__dirname, 'views'), {
  extname: '.njk',
  noCache: process.env.NODE_ENV !== 'production',
  throwOnUndefined: true,
  filters: {
    json: function (str) {
      return JSON.stringify(str, null, 2);
    },
    upperCase: str => str.toUpperCase(),
  },
  globals: {
    version: 'v3.0.0',
  },
}));

*/

// Inspired by:
// https://github.com/ohomer/koa-nunjucks-render/blob/master/index.js
// https://github.com/beliefgp/koa-nunjucks-next/blob/master/index.js

const Promise = require('bluebird');
const nunjucks = require('nunjucks');

function njk(path, opts) {
  const env = nunjucks.configure(path, opts);

  const extname = opts.extname || '';

  const filters = opts.filters || {};
  //console.time('benchmark');
  const f = Object.keys(filters).length;
  let i = 0;
  while (i < f) {
    env.addFilter(Object.keys(filters)[i], Object.values(filters)[i]);
    i += 1;
  }
  //console.timeEnd('benchmark');

  const globals = opts.globals || {};
  const g = Object.keys(globals).length;
  let j = 0;
  while (j < g) {
    env.addFilter(Object.keys(globals)[j], Object.values(globals)[j]);
    j += 1;
  }

  return (ctx, next) => {
    ctx.render = (view, context = {}) => {
      context = Object.assign({}, ctx.state, context);
      return new Promise((resolve, reject) => {
        env.render(`${view}${extname}`, context, (err, res) => {
          if (err) {
            return reject(err);
          }
          ctx.body = res;
          return resolve();
        });
      });
    };
    return next();
  };
}

module.exports = njk;