How to Use Environment Variables in Express

In web development, it is common to have sensitive information and configuration settings that should not be hard-coded directly into the source code. Examples of such sensitive data include database connection strings, API keys, and authentication credentials. To keep this information secure and separate from the codebase, we can make use of environment variables.

Environment variables are dynamic values that can be set on the operating system or within the execution environment. They provide a way to store configuration settings outside of the application’s code and can be accessed by the application at runtime.

In this tutorial, we will learn how to use environment variables in an Express.js application. We will explore how to set up and access environment variables, and see some practical examples of their usage.

Setting Up Environment Variables

To begin using environment variables in an Express.js application, follow these steps:

Step 1: Install the dotenv package

The dotenv package allows us to load environment variables from a .env file into process.env. Start by installing it using npm:

npm install dotenv

Step 2: Create a .env file

Create a new file in the root directory of your Express.js project called .env. This file will hold your environment variables in a key-value format.

DATABASE_URL=mongodb://localhost/mydatabase
API_KEY=your_api_key_here

Note that the values assigned to the variables should not be surrounded by quotes.

Step 3: Load environment variables

To load the environment variables from the .env file, require the dotenv package at the beginning of your application’s entry point file. Typically, this is the file where you initialize your Express.js app (e.g., index.js or app.js).

require("dotenv").config();

This will load the variables defined in the .env file into process.env, making them accessible throughout your application.

Accessing Environment Variables

Once the environment variables are loaded, you can access them using the process.env object. For example, if you have a variable named DATABASE_URL, you can access its value as follows:

const dbUrl = process.env.DATABASE_URL;
console.log(dbUrl); // Output: mongodb://localhost/mydatabase

You can use the variables in any part of your Express.js application where they are needed, such as connecting to a database or using an API key.

Practical Examples

Let’s explore a couple of practical examples to see how environment variables can be used in an Express.js application.

Example 1: Database Configuration

Suppose you have an Express.js application that needs to connect to a MongoDB database. Instead of hard-coding the database connection string in your code, you can store it as an environment variable.

1. Create a .env file and add the following line:

DATABASE_URL=mongodb://localhost/mydatabase

1. In your Express.js application, access the database URL using the environment variable:

const mongoose = require("mongoose");
const dbUrl = process.env.DATABASE_URL;

mongoose
  .connect(dbUrl, { useNewUrlParser: true, useUnifiedTopology: true })
  .then(() => {
    console.log("Connected to the database");
  })
  .catch((error) => {
    console.error("Error connecting to the database:", error);
  });

Example 2: API Key

Suppose you are integrating your Express.js application with a third-party API that requires an API key. Instead of exposing the API key directly in your code, you can store it as an environment variable.

1. Create a .env file and add the following line:

API_KEY=your_api_key_here

1. In your Express.js application, access the API key using the environment variable:

const axios = require("axios");
const apiKey = process.env.API_KEY;

axios
  .get("https://api.example.com/data", {
    headers: {
      Authorization: `Bearer ${apiKey}`,
    },
  })
  .then((response) => {
    console.log("API response:", response.data);
  })
  .catch((error) => {
    console.error("Error fetching data from API:", error);
  });

Exercise

Now it’s time to test your understanding of using environment variables in Express.js. Here’s a simple exercise for you:

Exercise: Create an Express.js application that uses environment variables to store the following information:

• Database connection string (DATABASE_URL)
• Secret key for session management (SESSION_SECRET)

1. Set up the dotenv package and load the environment variables from a .env file.
2. Connect to a MongoDB database using the DATABASE_URL environment variable.
3. Use the SESSION_SECRET environment variable as the secret key for session management in Express.js.
4. Implement a route that retrieves some data from the database and returns it as a response.

You can test your application by starting the server and accessing the route using a web browser or a tool like cURL.

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By following the steps and examples outlined in this tutorial, you should now have a good understanding of how to use environment variables in an Express.js application.

Remember to always keep sensitive information separate from your codebase for better security and flexibility.

Happy coding!