node-decorators

What are Decorators

Just like we have @annotations in Java Universe (Spring), we have @decorators in NodeJS (TypeScript) universe. These 2 enable us to carve out redundant code like caching, logging, validity of parameters etc.

From TypeScriptLang

A Decorator is a special kind of declaration that can be attached to a class declaration, method, accessor, property, or parameter. Decorators use the form @expression , where expression must evaluate to a function that will be called at runtime with information about the decorated declaration.

Why use Decorators

1. Abstract out redundant code
2. Keep business logic clean
3. Improve developer productivity

Look at this basic example

const getUsernameById(String userId){
  const userName = CACHE.get("bucket", userId);
  if(!_.isNil(userName)) {
    return userName;
  }
  
  const user = UserModel.getById(userId);
  CACHE.set("bucket", userId, user.name);
  Log.info(
    method: "getUsernameById"
    key_1: "userId",
    key_1_value: userId,
    key_2: "userName",
    key_2_value: userName
  )
  return user.name;
}

This can be reduced to following using decorators

@Cache
@Log
const getUsernameById(String userId){
  const user = UserModel.getById(userId);
  return user.name;
}

How to use this project

Prerequisites

• node >= v14.18.2
• npm >= 6.14.15

Running the tests

git clone https://github.com/thekosmix/node-decorators
cd node-decorators
npm i
npx ts-node test.ts

Features

• @Cache: Caches the result of a method. The cache key is generated by concatenating the method's arguments.
• @Log: Logs information about a method's execution, with options to log request and response data.
• @Length: Validates the length of a class property.
• @Async: Executes a method asynchronously.
• @Rest: Exposes a method as a REST API endpoint.