# Modes and Environment Variables

# Modes

Mode is an important concept in Vue CLI projects. By default, there are three modes:

  • development is used by vue-cli-service serve
  • test is used by vue-cli-service test:unit
  • production is used by vue-cli-service build and vue-cli-service test:e2e

You can overwrite the default mode used for a command by passing the --mode option flag. For example, if you want to use development variables in the build command:

vue-cli-service build --mode development

When running vue-cli-service, environment variables are loaded from all corresponding files. If they don't contain a NODE_ENV variable, it will be set accordingly. For example, NODE_ENV will be set to "production" in production mode, "test" in test mode, and defaults to "development" otherwise.

Then NODE_ENV will determine the primary mode your app is running in - development, production or test - and consequently, what kind of webpack config will be created.

With NODE_ENV set to "test" for example, Vue CLI creates a webpack config that is intended to be used and optimized for unit tests. It doesn't process images and other assets that are unnecessary for unit tests.

Similarly, NODE_ENV=development creates a webpack configuration which enables HMR, doesn't hash assets or create vendor bundles in order to allow for fast re-builds when running a dev server.

When you are running vue-cli-service build, your NODE_ENV should always be set to "production" to obtain an app ready for deployment, regardless of the environment you're deploying to.

NODE_ENV

If you have a default NODE_ENV in your environment, you should either remove it or explicitly set NODE_ENV when running vue-cli-service commands.

# Environment Variables

You can specify env variables by placing the following files in your project root:

.env                # loaded in all cases
.env.local          # loaded in all cases, ignored by git
.env.[mode]         # only loaded in specified mode
.env.[mode].local   # only loaded in specified mode, ignored by git

An env file simply contains key=value pairs of environment variables:

FOO=bar
VUE_APP_SECRET=secret

Note that only variables that start with VUE_APP_ will be statically embedded into the client bundle with webpack.DefinePlugin.

For more detailed env parsing rules, please refer to the documentation of dotenv. We also use dotenv-expand for variable expansion (available in Vue CLI 3.5+).

Loaded variables will become available to all vue-cli-service commands, plugins and dependencies.

Env Loading Priorities

An env file for a specific mode (e.g. .env.production) will take higher priority than a generic one (e.g. .env).

In addition, environment variables that already exist when Vue CLI is executed have the highest priority and will not be overwritten by .env files.

.env files are loaded at the start of vue-cli-service. Restart the service after making changes.

# Example: Staging Mode

Assuming we have an app with the following .env file:

VUE_APP_TITLE=My App

And the following .env.staging file:

NODE_ENV=production
VUE_APP_TITLE=My App (staging)
  • vue-cli-service build builds a production app, loading .env, .env.production and .env.production.local if they are present;

  • vue-cli-service build --mode staging builds a production app in staging mode, using .env, .env.staging and .env.staging.local if they are present.

In both cases, the app is built as a production app because of the NODE_ENV, but in the staging version, process.env.VUE_APP_TITLE is overwritten with a different value.

# Using Env Variables in Client-side Code

You can access env variables in your application code:

console.log(process.env.VUE_APP_SECRET)

During build, process.env.VUE_APP_SECRET will be replaced by the corresponding value. In the case of VUE_APP_SECRET=secret, it will be replaced by "secret".

In addition to VUE_APP_* variables, there are also two special variables that will always be available in your app code:

  • NODE_ENV - this will be one of "development", "production" or "test" depending on the mode the app is running in.
  • BASE_URL - this corresponds to the publicPath option in vue.config.js and is the base path your app is deployed at.

All resolved env variables will be available inside public/index.html as discussed in HTML - Interpolation.

TIP

You can have computed env vars in your vue.config.js file. They still need to be prefixed with VUE_APP_. This is useful for version info

process.env.VUE_APP_VERSION = require('./package.json').version

module.exports = {
  // config
}

# Local Only Variables

Sometimes you might have env variables that should not be committed into the codebase, especially if your project is hosted in a public repository. In that case you should use an .env.local file instead. Local env files are ignored in .gitignore by default.

.local can also be appended to mode-specific env files, for example .env.development.local will be loaded during development, and is ignored by git.