Using environment variables in React applications

For React applications using Vite

In React applications using Vite (e.g. those using @nx/vite:* executors), Nx includes the following variables in the build process:

  • Variables prefixed with VITE_, such as VITE_CUSTOM_VAR

You can read more about how to define environment variables in Vite here.

You can then use these variables in your application code like so: import.meta.env.VITE_CUSTOM_VAR.

Environment Variable Conflict between Nx and Vite

When using Nx with Vite, you may encounter an issue related to loading environment variables that can lead to unexpected behavior. This issue arises due to the way Nx and Vite handle environment files and configuration settings.

  1. Nx Environment Variable Loading: Nx loads environment variables from configuration names using the --configuration flag. This is the preferred method in Nx, especially when you have a default configuration specified in your project.json file for most targets. In our guide on how to define environment variables, you can see that if you're using the configuration option, then Nx will load .env.[configuration-name] files.

  2. Vite Environment Variable Loading: Vite loads environment files named .env.[mode] using the --mode flag.

The conflict occurs when you use the --configuration flag in Nx. In such cases, the --mode flag in Vite is ignored. For example, this behavior can be particularly confusing, as it may seem like you are always loading the development mode in Vite, instead of the expected one, if you're using the --configuration=development setting or if your default configuration is development.

The root cause of this issue is that Nx has already loaded variables from .env.[configuration]. So any variables defined in both Nx and Vite's .env.[mode] files will have their values overridden by the Nx-loaded values.


We recommend that developers adapt to the Nx way of handling environment variables and refer to our documentation on defining environment variables. This will help ensure consistent behavior and prevent conflicts when using Nx with Vite.

However, if you still want to use Vite's mode, you still can. To ensure seamless integration between Nx and Vite environment variables, you can establish a clear distinction between configuration and mode names. By assigning distinct names to both configuration and mode, you can eliminate any potential conflicts that may arise during environment variable loading. Additionally, consider defining custom configurations in your Nx workspace, each with a corresponding mode option. For example, you can create configurations like development, production, and staging, each with its respective mode set, like this:

1"configurations": { 2 "development": { 3 "mode": "development" 4 }, 5 "production": { 6 "mode": "production" 7 }, 8 "staging": { 9 "mode": "staging" 10 }, 11 "my-other-mode": { 12 "mode": "my-other-mode" 13 } 14} 15

That way, you can set the --configuration flag to development, production, or staging to load the corresponding .env.[configuration] file, and this will respect the mode set in the configuration.

Using environment variables in index.html

You cannot interpolate environment variables into your index.html file for React applications using Vite.

For non-Vite React applications

In React applications (e.g. those using the @nx/web:webpack executor or an inferred task that runs the Webpack CLI for building), Nx includes the following variables in the build process:

  • Variables prefixed with NX_PUBLIC, such as NX_PUBLIC_CUSTOM_VAR (when using the NxWebpackPlugin or the withNx plugins)

Defining environment variables can vary between OSes. It's also important to know that this is temporary for the life of the shell session.

Using environment variables in index.html

Nx supports interpolating environment variables into your index.html file for React and Web applications built with Webpack. This feature is available when using the NxWebpackPlugin or the withNx plugins.

Predefined Nx variable

Note that with the release of Nx 19, you won't be able to use predefined Nx variable on this link.

To interpolate an environment variable named NX_PUBLIC_DOMAIN_NAME into your index.html, surround it with % symbols like so:

1<html> 2 <body> 3 <p>The domain name is %NX_PUBLIC_DOMAIN_NAME%.</p> 4 </body> 5</html> 6