एनवायरनमेंट वेरिएबल और कॉन्फ़िगरेशन के तरीके

// Build config from defaults, then override via env when present
function buildConfig() {
  const defaults = {
    apiUrl: "https://api.example.com",
    port: 3000,
    debug: false
  };

  // env values are strings; parse to right types
  const apiUrl = readEnv("API_URL", defaults.apiUrl);
  const portStr = readEnv("PORT", String(defaults.port));
  const debugStr = readEnv("DEBUG", defaults.debug ? "1" : "0");

  return {
    apiUrl: apiUrl,
    port: Number.parseInt(portStr, 10),
    debug: debugStr === "1" || debugStr === "true"
  };
}

const cfg = buildConfig();
console.log("config:", cfg);

// Pass config into functions explicitly (easier to test)
function startApp(config) {
  // use values directly
  const mode = config.debug ? "debug" : "prod";
  return "Starting " + mode + " at " + config.apiUrl + " on :" + config.port;
}

console.log(startApp(cfg));

// Helpers to parse common env shapes safely
function toBool(s, fallback) {
  if (typeof s !== "string") return fallback;
  const v = s.trim().toLowerCase();
  if (v === "1" || v === "true" || v === "yes") return true;
  if (v === "0" || v === "false" || v === "no") return false;
  return fallback;
}

function toInt(s, fallback) {
  const n = Number.parseInt(s, 10);
  return Number.isFinite(n) ? n : fallback;
}

console.log("toBool:", toBool("yes", false), toBool("no", true));
console.log("toInt :", toInt("8080", 3000), toInt("oops", 3000));