Use process.env in Angular 5 environment

Update

Per the comments below the original answer was not entirely clear — Angular is built with Angular CLI, which is a node application, but you aren’t able to access process.env directly from within the app during that build process, as it’s not processed as a Node application.

The concepts stay pretty much the same, but it’s important to understand the above.

Original

You won’t have access to process.env at compile-time of the Angular code.

process.env is available to Node applications, which an Angular application is not.

You have several options:

1. Make a task of some sort in your build pipeline to update the environment file with the correct value if it truly needs to be dynamic.

2. Just hardcode it and make several environmental files to match each of your environments. You can specify your environments in your angular-cli.json.

Option number 2 sounds like it might be right for you. In that case, you want to put this in your angular-cli.json:

"environments": {
    "dev": "path/to/dev/env",
    "prod": "path/to/prod/env"
}

and build your app with ng build --env=prod.

Here is more in-depth information:
https://alligator.io/angular/environment-variables/