Build-time environment variable injection script for Angular apps

set-env.js

/* Generate environment.ts file using environment variables

Requires:
npm install --save yargs
npm install --save dotenv

Usage:
node set-env.js --env=dev

Put variables in a local .env file so they can be
read by `dotenv`.

Register more env variables for your app in the
`envConfigFile` template definition.
*/

const writeFile = require('fs').writeFile;
const argv = require('yargs').argv;
require('dotenv').config();

const environment = argv.env;
const isProd = environment === 'prod';

const targetPath = `./src/environments/environment.${environment}.ts`;
const envConfigFile = `\
// ${environment} environment
export const environment = {
  production: ${isProd},
  myVar: "${process.env.MY_VAR}",
};
`

writeFile(targetPath, envConfigFile, function (err) {
  if (err) {
    console.log(err);
  } else {
    console.log(`Output generated at ${targetPath}:`);
    console.log(envConfigFile);
  }
});