Add Accessing Env Vars In create-react-app as a react til

react/accessing-env-vars-in-create-react-app.md

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+# Access Env Vars In create-react-app
+
+Environment-specific configurations are an important part of most
+applications. You can access environment variables in your create-react-app
+code using `process.env`.
+
+There are a couple built-in environment variables, such as `NODE_ENV`.
+Anything custom that you want to provide must be prepended with
+`REACT_APP_`. If it isn't, that environment variable will be ignored with no
+warning.
+
+The following line of code
+
+```javascript
+const base_api_url = process.env.REACT_APP_BASE_API_URL;
+```
+
+will have access to whatever that value is in the environment when the
+server is started or the app is built.
+
+Set that value inline like so:
+
+```
+REACT_APP_BASE_API_URL="https://api.my_app.com" yarn start
+```
+
+[source](https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md#adding-custom-environment-variables)