Decorator

A Javascript decorator is an expression which returns a function and can take a target, name and property descriptor as arguments.

• You apply it by prefixing the decorator with an @ character and placing this at the very top of what you are trying to decorate.
• Decorators can be defined for either a class or property.

Decorators get called first before classes are compiled.

• In Javascript when we define a new class with methods, we are really just installing a descriptor on the object's prototype.

A decorator is just an expression that will be evaluated and has to return a function.

Readonly decorator

function readonly(target, key, descriptor) {
  descriptor.writable = false
  return descriptor
}

class Horse {
  @readonly
  neigh() console.log('*neigh!*')
}

Class decorators

@decorator is a function that returns a decorator.

• a decorator itself is a function that takes in a class and returns that same class.

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Backlinks

• Nestjs