使用 process.env.PORT 有什么用？

Question

When we set the environment variable PORT using something like set PORT=5000 then we are telling the program directly which port to use. So how is this any different from directly telling it to use port 3000?

Answer 1

Environment variables are used to simplify complexity and padronize values alongside one or many environments, for example, if your service runs on 2 environments, lets say qa and production, with environment variables you can simple write 2.env files and use diferent values for each one.

Answering your question, yes, if you set an environment variable for a port or set it in an in-code variable, in both ways you're telling the program what port to use. Well, for your code, doens't matter from where the port are beeing set.

So... Why you would do that using env variables?

Well, that's the main question I think, env variables provide a reliable way to:

• Change values without having to change many places alongside your code;
• Change values betwheen multiple environments;
• Make your app easier to setup and configurate;

Actually they can do more than it. You can check a nice reading about it here: https://medium.com/chingu/an-introduction-to-environment-variables-and-how-to-use-them-f602f66d15fa

A suggestion is, use env variables whenever you have to use one of these on your code:

• Execution mode (eg, production, development, staging, etc.)
• Domain names
• API URL/URI's
• Ports
• Public and private authentication keys (only secure in server applications)
• Group mail addresses, such as those for marketing, support, sales, etc. Service account names

But as you can see, it's not mandatory. Hope it can help you.