.gitignore

process.env.ts

environment.ts

import { process_env } from './process.env';

const api_url = process_env['API_URL'] || location.hostname;
const api_key = process_env['API_KEY'] || 'LOCAL-DEFAULT-KEY';

export const environment = {
  production: false,
  api_url,
  api_key
};

package.json

{
  ...
  "scripts": {
    ...
    "prestart": "node prestart.js",
    "start": "ng serve",
    ...
  },
...
}

prestart.js

#!/usr/bin/env node

const fs = require('fs');
const path = require('path');
const vars = require('./process.env').vars;

const env_vars = {};
vars.forEach(x => {
    if (vars.indexOf(x) !== -1) {
        env_vars[x] = process.env[x];
    }
});


const env_path = path.join(__dirname, 'src', 'environments', 'process.env.ts');
const env_str = JSON.stringify(env_vars, null, ' ');

fs.writeFileSync(env_path, `export const process_env = ${env_str};`);

process.exit(0);

process.env.js

exports.vars = [
  'API_URL',
  'API_KEY'
];