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Common "Gotchas"

Here are some common issues that you may run across and how to deal with them.

Errors with import or export in certain files

You may run across this dreaded error:

SyntaxError: Unexpected token import

...despite the fact that in some code, import and export works fine. This is caused by varying ways in which your application code is loaded. Some of it is loaded via node require statements, and some of it is transpiled/bundled first by webpack before being loaded. Generally speaking, only the code that is loaded through page entry points (/pages/**/*.js) is transpiled to ES5 modules. Files like these and their dependencies should be written as CommonJS-style modules because they're imported directly by node:

  • The Gasket config file (gasket.config.js)
  • Your store creator (including files it imports, like reducers, action constants, etc.) - typically store.js.
  • Lifecycle hooks (/lifecycles/*.js)
  • Plugins (/plugins/*.js)

Besides ES6 modules, any other Babel-supported features that are not directly supported by your node version should also be avoided.

Use @babel/register

If you need to use ES6 style modules for some of your server code, you can enable ES6 modules in your app code by adding @babel/register to your app. This will bind itself to node's require and automatically compile files on the fly.

First, install it to your app:

npm i @babel/register

Then include it at the top of your gasket.config.js

// gasket.config.js
+ require('@babel/register');

module.exports = {
  // config goes here
};

Requiring @babel/register in your gasket.config.js will ensure Babel transpilation begins at the earliest point in the loading process for your app code. It also ensures that @babel/register itself is not included in your webpack bundles.

It is important to note that your gasket.config.js must continue to use require and export using CommonJS syntax (e.g. module.exports =). Any subsequent files loaded, however, are free to use ES Modules syntax.

Additionally, any other special files directly expected by Gasket (e.g. store.js, /lifecycles/*.js, or /plugins/*.js) must also use CommonJS syntax. The reason being is that default exports will be transformed to have a .default property, which Gasket plugins won't be expecting or know how to handle.

For example, say you write store.js for @gasket/plugin-redux as ES6 module:

// store.js
import { configureMakeStore } from '@gasket/redux';
import reducers from './redux/reducers';

export default configureMakeStore({ reducers });

This will be transformed into something like:

'use strict';
const { configureMakeStore } = require('@gasket/redux');
const reducers = require('./redux/reducers').default;

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = function configureMakeStore({ reducers });

When the redux-plugin tries to load this using require, it won't know to use .default. See how are reducers import was transformed?

So, for these special files, continue to use module.exports.

Using with babel-plugin-add-module-exports

If you want to get around the .default behavior as mentioned above, you can use babel-plugin-add-module-exports which will add the module.exports if only the export default declaration exists.

⚠️This has not been thoroughly tested, however, so proceed with caution and report back any issues that may have been encounter.

npm i babel-plugin-add-module-exports
// gasket.config.js
require('@babel/register')({
+  plugins: ['add-module-exports']
});

module.exports = {
  // config goes here
};