typescript 50 lines · 6 steps

Validated, typed config in NestJS

A NestJS module validates environment variables at startup with Joi and exposes them through a typed, injectable service.

Explained by highlit
NestJS Intermediate configuration validation dependency-injection environment-variables fail-fast
1import { Module, Injectable } from '@nestjs/common';
2import { ConfigModule, ConfigService } from '@nestjs/config';
3import * as Joi from 'joi';
4 
5const validationSchema = Joi.object({
6 NODE_ENV: Joi.string().valid('development', 'production', 'test').default('development'),
7 PORT: Joi.number().default(3000),
8 DATABASE_URL: Joi.string().uri().required(),
9 JWT_SECRET: Joi.string().min(32).required(),
10 JWT_EXPIRES_IN: Joi.string().default('3600s'),
11});
12 
13@Module({
14 imports: [
15 ConfigModule.forRoot({
16 isGlobal: true,
17 cache: true,
18 envFilePath: [`.env.${process.env.NODE_ENV ?? 'development'}`, '.env'],
19 validationSchema,
20 validationOptions: { abortEarly: false },
21 }),
22 ],
23 providers: [AppConfigService],
24 exports: [AppConfigService],
25})
26export class AppConfigModule {}
27 
28@Injectable()
29export class AppConfigService {
30 constructor(private readonly config: ConfigService) {}
31 
32 get isProduction(): boolean {
33 return this.config.getOrThrow<string>('NODE_ENV') === 'production';
34 }
35 
36 get port(): number {
37 return this.config.getOrThrow<number>('PORT');
38 }
39 
40 get databaseUrl(): string {
41 return this.config.getOrThrow<string>('DATABASE_URL');
42 }
43 
44 get jwt(): { secret: string; expiresIn: string } {
45 return {
46 secret: this.config.getOrThrow<string>('JWT_SECRET'),
47 expiresIn: this.config.getOrThrow<string>('JWT_EXPIRES_IN'),
48 };
49 }
50}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Validating env vars at boot turns silent misconfiguration into a loud, immediate failure.
  2. 2Wrapping ConfigService in a typed service gives the rest of the app safe, autocompleted access to settings.
  3. 3Marking the config module global lets every feature read configuration without re-importing it.

Related explainers

java 
@Component
public class RegionCacheWarmer implements SmartInitializingSingleton {
 
    private static final Logger log = LoggerFactory.getLogger(RegionCacheWarmer.class);

Warming a Spring cache at startup

caching startup-hook dependency-injection
Intermediate 7 steps
typescript 
import { Controller, Param, Sse, MessageEvent } from '@nestjs/common';
import { Observable, interval, merge } from 'rxjs';
import { filter, map, takeWhile } from 'rxjs/operators';
import { JobService } from './job.service';

Streaming job progress with SSE in NestJS

server-sent-events reactive-streams rxjs
Intermediate 8 steps
java 
public final class EmailNormalizer {
 
    private static final Pattern EMAIL_PATTERN = Pattern.compile(
        "^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}$"

Normalizing email addresses in Java

validation regex normalization
Intermediate 8 steps
typescript 
import {
  Controller,
  All,
  Req,

Catch-all routes and error shaping in NestJS

exception-handling routing middleware
Intermediate 6 steps
python 
from datetime import date, timedelta
from typing import Annotated
 
from fastapi import APIRouter, Depends, Query

Validating date ranges with FastAPI dependencies

dependency-injection validation pydantic
Intermediate 6 steps
typescript 
import {
  ArgumentsHost,
  Catch,
  ConflictException,

Turning TypeORM lock errors into 409s in NestJS

exception-handling optimistic-locking http-status
Intermediate 6 steps

Share this explainer

Here's the card — post it anywhere.

Validated, typed config in NestJS — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code