What are Decorators in Typescript
Just like we have @annotations in Java Universe (Spring), we have @decorators in Node.js (TypeScript) universe.
These 2 enable us to abstract out redundant and non business related code like caching, logging, validity of parameters and a lot more.
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 to use Decorators
- Abstract out redundant code
- Keep business logic clean
- Boost developer productivity
- Keep Non-functional things like caching/logging/validations standardise across services
Look at this basic example
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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;
}
Using decorators, it can be reduced to
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@Cacheable
@Loggable
const getUsernameById(String userId){
const user = UserModel.getById(userId);
return user.name;
}
PS: These implementations/naming can be different for others, but gist is same
What all entity Decorators can support
Just like Java, typescript support class method/function and property level decorators and many more:
- Class decorators: Can be used for creating components or singleton objects.
- Method decorators: Can be used for logging request response of a method, caching params and returned value, etc
- Property decorators: Can be used for validating a property value on assignment or initialisation
A detailed description can be found here.
How can I start with Decorators for my project
Trust me when I say this, it’s very easy to implement. It’ll be one of those projects which will give you the highest ROI on engineering investments.
It took me few hours to implement @Cache and @Log for a test project. The working project can be found here.
What’s next
To create an npm library which out of the box will support these annotations just like spring-boot. Do give a pull request if you have any suggestions.