Introduction to Express Dotenv for Environment Variables. In this video, I'm going to cover how to handle environment variables in the Express application using the dotenv npm package. To begin in the terminal, I will type npm install dotenv. In order to use dotenv, I need to create a dotfile for it. I will click on 'New File', the file name begins with a period, env. Now dotfiles could be configuration files or other files and they all begin with a period. By default, dotfiles are hidden by your operating system. Now for this demonstration, I'm going to set the port used by this Express application as an environment variable. Inside of the dotenv file, I will type port = 3001. Now, one thing about environment variables is they are meant to be secure. I do not want to include them as part of this Git repository. I'm going to create a Git ignore file. Once again, new file beginning with a dot gitignore. Inside of the file I will add dotenv.

Now Git will ignore this file as part of any commits. Next, I need to go to the server.js file and configure dotenv. In order to make this work, I need to require the dotenv package and execute its convict method. Near the top, I will type require.env.config. Note I'm not setting the require statement equal to a variable, I'm just executing the package. Earlier when I created the dotenv file, I set the port as an environment variable. I'm going to change the port variable here in the server file to be equal to that environment variable. I'm going to replace 3001 with process.env.PORT, and port is in all caps to match how it was written in the dotenv file. So, what is this process.env.PORT that is attached to the port environment variable? 

I'm going to dive a little deeper into node in the process object. The process object provides information about and control over the current NodeJs process. As part of this process object, there's also a sub-object property known as env. Process.env provides a user's environment. One can figure the dotenv npm package will attach the information inside of the dotenv file as additional properties to process.env. Returning back to the server.js file, after the process.env.PORT environment variable, I'm going to add the OR operator and provide a secondary value of 4000. I'm using the OR operator as part of this declaration as a fail-safe. If for some reason the environment variable doesn't exist or is undefined, the 4000 will become the new port value. I'm only using 4000, in this case, to differentiate this value from 3001.

The port number you use is whatever works for your development environment. Now, this is ready to test out. So, down below in the terminal, I will type node server.js and hit 'Enter' and the server has started on the terminal running on port 3001. So, this works. And that's it, thanks for watching at Cloud Academy.