Solution to Problems that Beginners Encounter ~React/Deploy~

I've been learning React only for three weeks, but I've had so many problems. I'll share one of them I encountered while I was deploying my project. It was not the same way I usually do since this time I was using API.

The project was to create a weather app using OpenWeatherMap, push the code to GitHub and deploy it to Netlify.
I hid the API key in a ".env" file with a variable name, just like this: VARIABLE_NAME_FOR_API = abcde12345

Here is what I needed to do:

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Netlify

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(1) Set Environment Variables
Deploys > Deploy settings > Environment
> Environment variables > Edit variables

 Key => VARIABLE_NAME_FOR_API
 value => abcde12345

(2) Set Build Command
Deploys > Deploy settings > Continuous Deployment
> Build settings > Build command

Build command => CI= yarn run build

* You can change 'yarn' to 'npm' if you're using npm
* Make sure it is capital i, and there's no space
  between "CI" and "=". I typed "CI = yarn run build" 
  and failed so many times.

I hope this will help those who have the same problem.