A walkthrough the main principles to reach solid NodeJS Applications with TypeScript language, Jest as Test Runner and NestJS as framework for structure.

1. Solid NodeJS
with TypeScript, Jest & Nest

2. “We build our computer systems
the way we build our cities:
over time, without a plan, on top of ruins.”
Ellen Ullman

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Flexibility
Its multi-paradigm nature, dynamic type
system and minimal core allow great flexibility.
Ecosystem
Great system with largest amount of
packages and best evolution.
Ubiquity
Presence both in client and server, along with
mobile environment and almost everywhere.
JavaScript

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Modularity
Keep simple parts short,
connected with clean interfaces.
Composition
Make those independent packages
work together to build applications
Simplicity
JavaScript succinct syntax and flexibility,
along with Node inherent asynchrony
NodeJS

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Lack of common architecture
Different approaches for directory and file structure,
and even module design.
Fragile execution
Input / Output non-standard type validation,
lack of testable parts because of coupling and derived
problems from lack of standards.
Problematic growth
Hard to scale and distribute work among
different developers and teams.
Medium to Large NodeJS Applications
What’s the STRUCTURE?
How do I get ROBUSTNESS?
What if I need SCALABILITY?
Application Issues

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Jest
Testing complete solution,
with zero config, fast execution,
and built-in coverage
.
Nest
Framework based on
combination of OOP/FP/FRP,
DI and building blocks.
TypeScript
JavaScript that scales
through latest features
and solid type static analysis.
Weapons
Solutions for Robustness, Scalability and Structure

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Why TypeScript?
๏ Types are optional (ideal for
validation)
๏ Type inference for static analysis
and tooling
๏ Interfaces for solid components
๏ Advanced ESNext features in
Development
๏ Compiles to clean, efficient,
compatible JavaScript

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Why Jest?
๏ Complete Testing Solution
๏ Minimum configuration
๏ Fast parallelization of tests across
workers
๏ Selective execution when
watching
๏ Built-in code coverage report with
Istanbul
๏ Snapshot Testing included

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Application Architecture
Nest provides building blocks around a execution
context to give a common architecture, that includes
controllers, modules, pipes, guards, etc.
Middleware structure
Built on top of Express, it leverages the
middleware capabilities of this framework..
Dependency Injection
All elements in Nest are defined around
DI principles, so services, modules, controllers,
all can be injected and thus easily testable.
Platform-agnostic
Reusable pieces that can be used in
different contexts, like GraphQL, Microservices
or Websockets..
Nest

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• Starter with TypeScript
• V5 is coming (beta) with
dedicated CLI
• Basic structure with
conventions
• Main entry point
First steps

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๏ Each Part of the Application
๏ Can be only one: Root Module
๏ Domain Bounded Contexts
๏ Module Decorator describes:
➡ Imports: Other modules
➡ Controllers: Created by the module
➡ Components/Providers: Instantiated and shared
across the module
๏ Modules are Singletons so they are shared.
Modules

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Every Module can Import
and Export other Modules
Admin ModuleUsers Module
Application Module
Stats ModuleBilling ModuleChat Module Game Module

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Example

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Controllers
๏ Request Handlers and Response Generators
๏ Must be declared associated to a Module
๏ Metadata in decorator defines prefix like @Controller(‘users’)
๏ Two approaches to handle Response:
➡ Nest: Returns Array or Object automatically as JSON
➡ Express: Injected through @Res() decorator.
Allow express-like response manipulation.
๏ POST handler can use Data Transfer Object (DTO)

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Example

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Components / Providers
๏ Services, Factories, Helpers, etc
๏ They can be Injected into Controllers or
other Components / Providers through constructor
๏ Any complex task performed into Controllers
๏ Pattern of reusability and modularity
๏ Plain TypeScript Classes

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Example

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Middlewares
๏ Function called before the Route Handler
๏ Have access to Request, Response and Next handler
๏ Same capabilities as express middlewares:
➡ Execute code before continuing: And then call next()
➡ Make changes to Request & Response
➡ End Request-Response cycle
๏ Can be defined:
➡ For specific paths
➡ For specific Controllers

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Example

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Exceptions
๏ Global Exception Filter for Unhandled Errors: 500 Server Error
๏ Built-in HttpException that when thrown by handler
it transforms to proper JSON response
๏ A good practice is to create your own Exception Hierarchy with
exceptions inherited by the HttpException class
๏ Nest offers several built-in HTTP Exceptions like:
BadRequestException, UnauthorizedException,
NotFoundException, ForbiddenException, etc

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Example

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Validation
๏ Validation is done through a specific Pipe
๏ Pipes are classes that implement the PipeTransform Interface
๏ A Pipe transforms the input data to desired output before Route Handler
๏ ValidationPipe is a built-in Pipe
๏ Data Transfer Object (DTO) is required to receive the @Body()
๏ Class-Validator library allow decorator-based validation on DTO definition

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Example

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Testing with Jest
๏ Every building block in Nest (Components, Controllers, etc) are simple decorated classes
๏ As every dependency is injected through constructor, they are easy to mock
๏ Recommendation is to keep your test files near the implementation
๏ Recommendation is always isolated tests
๏ Test class is a utility with createTestingModule() that takes module metadata and creates
a TestingModule instance.

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Example

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Example

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Database Access
๏ Nest uses by default the standard TypeORM for Object Relational Model
๏ Mongoose use the built-in @nestjs/mongoose package

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Example

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GraphQL
Module for GraphQL
server with Apollo
Websockets
Decorators to include
WS transport
Microservices
NestJS microservices are
TCP interconnected services
Platform-agnosticism allow building apps
with several transport layers and contexts.

30. Always bet on JavaScript.
Let’s make JS applications more solid.
Let’s do it on scale.
“It's never on how difficult
is to write bad code,
it's on how easy is
to write great code.”
@yonatam

31. Thank you
No real requests were damaged during this talk.