JS decorators example

readonlyDecorator.ts

function readonly(target: any, name: string, descriptor: TypedPropertyDescriptor<() => void>) {
  descriptor.writable = false
  return descriptor
}

class Example {
  a: number

  @readonly
  b() {}

  constructor(a: number) {
    this.a = a
  }
}

const example = new Example(0)
example.a = 1
example.b = 2
// [ERR]: Attempted to assign to readonly property.