postcss-cssnext not processing output

Question

I'm trying to setup postcss-cssnext and must be missing something because when I run npm run postcss my output file is created but it looks like the input file (except for some whitepace differences). My postcss.config.js file is being loaded but the features are not processing. What am I missing?

postcss.config.js

var postcss = require('postcss');
var cssnext = require('postcss-cssnext');

postcss([
  cssnext({})
]);

package.json

{
  "scripts": {
    "postcss": "postcss input.css -o output.css"
  }
}

Answer 1

Problem solved by exporting to module.exports

var postcss = require('postcss');
var cssnext = require('postcss-cssnext');

module.exports = postcss([
  cssnext({})
]);