How To Deploy A Web App To Heroku

2 min read

This is a quick blog on how I deployed my weather manager app to Heroku.

Deploying took longer than anticipated, due to an issue I was experiencing with dotenv-webpack and dotenv in a production environment. The following error kept popping up when deploying to Heroku:

1Error: failed to load ./.env

Thanks to one of my mentors, Dan, for helping me to figure out what was going on! As this issue has been resolved, this blog will outline the steps in an order that should not cause errors when deploying.

For reference, here’s how my weather manager files are organised. There are hidden files:

  • ./dist contains main.js

  • .env (which contains my API key) is in the root directory

Step 1: Express.js — web app framework

  • Create server.js in the root directory, and add the following code:
1const express = require("express");
2const path = require("path");
3const port = process.env.PORT || 8080;
4const app = express();
6app.use(express.static(__dirname + '/dist'));
8app.get('*', (req, res) => {
9 res.sendFile(path.resolve(__dirname, 'index.html'));
  • Run npm install express

Key points

  • __dirname is the directory where server.js is

  • __dirname + ‘/dist' is the current directory from where main.js is running

Step 2: Create

This step is important if you have dotenv-webpack installed. If installed then in webpack.config.js, dotenv-webpack is required:

1const path = require("path");
2const Dotenv = require("dotenv-webpack");
4module.exports = {
5 entry: "./src/index.js",
6 mode: "development",
7 output: {
8 filename: "main.js",
9 path: path.resolve(__dirname, "dist"),
10 },
11 node: {
12 fs: "empty",
13 },
14 plugins: [new Dotenv()],

This is fine for development, but doesn’t seem to work well for production. Therefore, a similar file is needed for production only, which doesn’t contain references to dotenv-webpack.

  • Create a copy of webpack.config.js in your root directory and name it

  • In, remove references to dotenv-webpack, and replace it with the following:

1const path = require("path");
2const webpack = require("webpack");
4module.exports = {
5 entry: "./src/index.js",
6 mode: "production",
7 output: {
8 filename: "main.js",
9 path: path.resolve(__dirname, "dist"),
10 },
11 node: {
12 fs: "empty",
13 },
14 plugins: [
15 new webpack.DefinePlugin({
16 "process.env": {},
17 }),
18 ],
  • Under scripts in package.json, add:
1"scripts": {
2 "start": "node server.js",
3 "heroku-postbuild": "webpack --config"

As a result, Heroku will use the file, rather than the webpack.config.js file.

  • Set the version of npm and Node.js by adding the below to package.json:
1"engines": {
2 "node": "11.6.0",
3 "npm": "6.5.0"

Step 3: Only require dotenv when NODE_ENV is set to development

  • Assuming dotenv is also installed, add the following to server.js, just under const app = express();
1if (process.env.NODE_ENV == 'development')
2require('dotenv').config({ silent: true });

Step 4: Set dotenv-webpack and dotenv as devDependencies

  • For dotenv-webpack and dotenv to be required during development only, run the following:
1npm install dotenv --save-dev
2npm install dotenv-webpack --save-dev

Step 5: Deploying to Heroku

  • Sign up to Heroku

  • Install Heroku CLI

  • Log into Heroku via the terminal with heroku login

  • Run heroku create to create your app on Heroku. An app name will be generated

  • Reinitialise the project by running git init

  • Set a Heroku remote branch by heroku git:remote --app [your-heroku-app-name]

  • Set your environment variables — or config vars as they’re referred to in Heroku. Here’s how I set my API key for openweathermap: heroku config:set API_KEY=myapikey3902e92e802e8

  • Git add and commit

  • Push to Heroku with git push heroku master

And that’s it (hopefully)!

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