Author: John Au-Yeung

To run Node.js app with ES6 features enabled, we set the presets option.

For instance, in package.json, we write

{
  "dependencies": {
    "babel-cli": "^6.0.0",
    "babel-preset-es2015": "^6.0.0"
  },
  "scripts": {
    "start": "babel-node --presets es2015 app.js"
  }
}

to add the babel-preset-es2015 package.

And we set the --presets option when we run babel-node to enable the ES6 features.

To read and write a text file in TypeScript and Node.js, we call the readFileSync function.

For instance, we write

import { readFileSync } from "fs";

const file = readFileSync("./filename.txt", "utf-8");

to call readFileSync to read filename.txt into a Unicode string.

To fix Node.js: SyntaxError: Cannot use import statement outside a module error, we use CommonJS modules.

For instance, we write

module.exports.func = () => {
  console.log("Hello World");
};

to define the func function and export it in mod.js.

Then we write

const myMod = require("./mod");
myMod.func();

to call require to require mod.js.

And we call myMod.func to call the function.

To call Node.js "require" function and parameters, we export a function.

For instance, we write

module.exports = (options) => {
  const app = options.app;
  const param2 = options.param2;
};

in lib.js to export a function.

Then we write

require("lib.js")({ app, param2 });

to require the lib.js file and call the function that’s imported.

To toggle between multiple .env files like .env.development with Node.js, we use the dotenv library.

For instance, we write

require("dotenv").config({ path: `.env.${process.env.NODE_ENV}` });

to call config with an object with the path property to point to the .env file path we want to use.

process.env.NODE_ENV is the NODE_ENV environment variable value.