next-branch-env

Branch environments for Next.js deployments on Vercel.

For example, if you need to create a staging environment for your Vercel deployments, you can use this library to make the STAGING_SECRET environment variable (defined in your Vercel Project Settings) available as SECRET in Vercel deployments deployed from your staging branch.

See next-branch-env-app for a demo Next.js application that uses this library.

Uses next-env for environment variable injection.

Installation

In your Next.js project:

npm i next-branch-env

or

yarn add next-branch-env

How it works

The library finds your deployment branch in your Vercel deployment environment and rewrites variables prefixed or postfixed with that branch name. The branch name must be an uppercase prefix or postfix followed by or preceded by an underscore _.

All environment variables in the Node.js build process are made available to the Next SSR server. Only environment variables beginning with NEXT_PUBLIC_ are made available to (are statically embedded in) the Next javascript bundle at build time. Note: STAGING_NEXT_PUBLIC_ID is made available as NEXT_PUBLIC_ID in staging branch deployments, but NEXT_PUBLIC_STAGING_ID is not.

Vercel Configuration

For this to work with your git-configured Vercel deployments:

• 'Automatically expose System Environment Variables' must be checked in your Vercel Project Settings.
• The Vercel environment (i.e. Production, Preview, and/or Development) assigned to your branch environment variables must include the relevant branch's deployments. For example, staging environments only see environment variables set for the Preview environment, so make sure that e.g. STAGING_SECRET is defined as a Preview environment variable in your Vercel Project Settings. Otherwise, this library will not see it.

Usage

Minimal Configuration

If you don't have to integrate with an existing Next.js configuration file, add the following next.config.js to your root directory (adjacent to package.json), and if everything is configured appropriately on Vercel, your branch-specific environment variables (defined in your Vercel Project Settings) will be made available to your branch deployments.

// next.config.js
module.exports = require('next-branch-env')()()

To see what exactly is happening here, you can run the following example config file directly

// next.config.js
process.env.STAGING_SECRET = 'f5b73b88d0d9d57c831d59c5aa9b09af' // set this in Vercel Project Settings
module.exports = require('next-branch-env')()()
console.log('SECRET =', process.env.SECRET) // SECRET = f5b73b88d0d9d57c831d59c5aa9b09af

with

BRANCH=staging node next.config

See the Options section below for more on what BRANCH=staging does.

Extended Configuration

If you need to integrate with your existing Next.js configuration, the following next.config.js file should help.

const withNextBranchEnv = require('next-branch-env')({
  // next-branch-env options
  // next-env default overrides
})

module.exports = withNextBranchEnv((phase, defaultConfig) => {
  // your next.js configuration
  return defaultConfig
})

Local Development Branches

If you want to inject the environment for your current local git branch, you can setup your package.json scripts as follows.

{
  "scripts": {
    "dev": "BRANCH=$(git branch --show-current 2>/dev/null||true) next dev",
    "build": "BRANCH=$(git branch --show-current 2>/dev/null||true) next build",
    "start": "BRANCH=$(git branch --show-current 2>/dev/null||true) next start"
  }
}

This should ease local development if you want to sync your local .env file with Vercel's backend with via vercel env pull. The 2>/dev/null||true ignores the fatal error that occurs if you're not currently in a git repo (e.g. when deploying to Vercel). See next section for more on how this works.

Options

next-branch-env exports a function

const withNextBranchEnv = require('next-branch-env')(options)

which accepts options that include

const options = {
  skip: false, // skip rewrite if variable already exists, rather than overwrite
  expose: 'NEXT_PUBLIC_BRANCH', // expose branch name as NEXT_PUBLIC_BRANCH env variable (remove NEXT_PUBLIC_ to make private or just set to false)
  verbose: true, // log rewrites (values are not exposed)
  branch: 'string', // if a branch is not found in env, you can supply your own (setting this with an env var is probably more convenient — see below)
  ...nextEnvOptions, // options for next-env
}

Rather than passing in a branch parameter, you can define a BRANCH or GIT_COMMIT_REF variable in your environment. next-branch-env will use this as a fallback, if a Vercel git provider (Github, Gitlab, or Bitbucket) is not found, as shown in the above examples.

By default, the exposure of environment variables matches Vercel's prefix convention: public variables need to be prefixed with NEXT_PUBLIC_. You can override these defaults by passing next-env options as next-branch-env options. Be careful not to expose sensitive data! Don't do this unless you know what you're doing.