The twelve-factor app stores config in environment variables (often shortened to env vars or env). Env vars are easy to change between deploys without changing any code. - The Twelve-Factor App
npm install --save-dev @runtime-env/cli-
Create a JSON-schema file and define your environment variables:
.runtimeenvschema.json{ "type": "object", "properties": { "TITLE": { "type": "string" } }, "required": ["TITLE"] } -
Using environment variables in your code:
index.jsdocument.body.innerHTML = globalThis.runtimeEnv.TITLE;
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Set environment variables in your terminal:
export TITLE="Hello Runtime Env"
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Use the
runtime-envCLI to generate a JavaScript file:npx --package @runtime-env/cli runtime-env gen-js --output-file runtime-env.js
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Import the generated file before importing the entry point:
index.html<!doctype html> <html> <body> <script src="./runtime-env.js"></script> <script src="./index.js"></script> </body> </html>
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Open
index.htmlin your browser, and you will seeHello Runtime Envin the console. -
Set a new environment variable, regenerate the JavaScript file, and refresh the page:
export TITLE="Yo Runtime Env" npx --package @runtime-env/cli runtime-env gen-js --output-file runtime-env.js
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That's it! You don't need to rebuild your app to update the environment variables anymore.
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Create a JSON-schema file:
.runtimeenvschema.json:{ "type": "object", "properties": { "TAG_ID": { "type": "string" }, "FIREBASE_CONFIG": { "type": "object", "properties": { "apiKey": { "type": "string" }, "authDomain": { "type": "string" } }, "required": ["apiKey", "authDomain"] } }, "required": ["TAG_ID", "FIREBASE_CONFIG"] }You could use other file name by running
npx -p @runtime-env/cli runtime-env --schema-file ....Runtime-env uses Ajv to parse your JSON-schema.
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Configure your package.json, Dockerfile, etc. to generate, and interpolate files:
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To generate a JavaScript file which contains the environment variables, you will execute
runtime-env gen-js:$ npx -p @runtime-env/cli runtime-env gen-js --output-file runtime-env.js
// runtime-env.js globalThis.runtimeEnv = { TAG_ID: "G-ABCD12345", FIREBASE_CONFIG: { apiKey: "AIzaSk2CngkeAyDJr2BhzSprQXp8PsZs3VFJFMA", authDomain: "example.firebaseapp.com", }, };
And make sure to import the generated file before importing the entry point:
<!-- index.html --> <script src="/runtime-env.js"></script> <script src="/index.js"></script>
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If you are using TypeScript, you can also generate a declaration file by running
runtime-env gen-ts:$ npx -p @runtime-env/cli runtime-env gen-ts --output-file runtime-env.d.ts
// runtime-env.d.ts // type DeepReadonly<T> = ... declare global {
var runtimeEnv: RuntimeEnv; } export type RuntimeEnv = DeepReadonly<{ TAG_ID: string; FIREBASE_CONFIG: { apiKey: string; authDomain: string; }; }>; -
For
index.htmland other non-JavaScript files, if needed, you can runruntime-env interpolate:$ npx -p @runtime-env/cli runtime-env interpolate --input-file index.html --output-file index.html
<script async src="https://www.googletagmanager.com/gtag/js?id=G-ABCD12345" ></script>
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Further setups:
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You NEED to set up your web server to stop runtime-env.js to be cached by browser or CDNs.
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To use runtime-env on systems that don't have Node.js installed, you'll need to pack
runtime-envCLI into a single runnable file. Here's how you can do it:-
Make a single runnable app using NodeJS's Single Executable Applications feature (experimental).
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Pack runtime-env into a runnable file using pkg:
$ pkg ./node_modules/@runtime-env/cli/bin/runtime-env.js --target node18-alpine-x64 --output runtime-env
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If you're making a PWA (Progressive Web App), you HAVE TO set up your ServiceWorker to choose the right way to cache runtime-env.js.
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$ npx -p @runtime-env/cli runtime-env --helpUsage: runtime-env [options] [command] Options: -V, --version output the version number --global-variable-name <globalVariableName> specify the global variable name (default: "runtimeEnv") --schema-file <schemaFile> specify the json schema file to be loaded (default: ".runtimeenvschema.json") --watch turn on watch mode (default: false) -h, --help display help for command Commands: gen-js [options] generate a JavaScript file that includes environment variables within an object, making them accessible through the globalThis property gen-ts [options] generate a TypeScript file that provides the corresponding type definitions for the JavaScript file generated by the gen-js command interpolate [options] perform template interpolation by substituting environment variables help [command] display help for command -
$ npx -p @runtime-env/cli runtime-env gen-js --helpUsage: runtime-env gen-js [options] generate a JavaScript file that includes environment variables within an object, making them accessible through the globalThis property Options: --env-file <envFile...> set environment variables from supplied file (requires Node.js v20.12.0) (default: []) --output-file <outputFile> specify the output file to be written instead of being piped to stdout -h, --help display help for command -
$ npx -p @runtime-env/cli runtime-env gen-ts --helpUsage: runtime-env gen-ts [options] generate a TypeScript file that provides the corresponding type definitions for the JavaScript file generated by the gen-js command Options: --output-file <outputFile> specify the output file to be written instead of being piped to stdout -h, --help display help for command -
$ npx -p @runtime-env/cli runtime-env interpolate --helpUsage: runtime-env interpolate [options] perform template interpolation by substituting environment variables Options: --env-file <envFile...> set environment variables from supplied file (requires Node.js v20.12.0) (default: []) --input-file <inputFile> specify the input file to be loaded instead of being read from stdin --output-file <outputFile> specify the output file to be written instead of being piped to stdout -h, --help display help for command
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For JavaScript, you can read environment variables through the
globalThisproperty:// Syntax: <globalVariableName>.<environmentVariableName> initializeApp(runtimeEnv.FIREBASE_CONFIG);
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For interpolation, you can use environment variables by a template:
<!-- Syntax: <%= <globalVariableName>.<environmentVariableName> %> --> <script async src="https://www.googletagmanager.com/gtag/js?id=<%= runtimeEnv.TAG_ID %>" ></script>