Side effect of decorator

🔎 Search Terms

"decorator" "field decorator" "side effect" "decorator side effect"

🕗 Version & Regression Information

• This changed between versions 5.0 and 5.2
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about decorators

⏯ Playground Link

https://www.typescriptlang.org/play?#code/MYewdgzgLgBAYgSwKYBsAmARJoBOBDKEHGAXhgAoo8cBzJKALhgFcw0kAzBMJNAGhigwUJAA9GMAMIo8ECIlSZsRAkUngR4gJSkAfDADeAXwBQJ4DLkwACtSTDDJmIPDQczYIRzlqNAIxMbtw0Ar4ATIFQOMGhtADMkdFgNDoGTs4wAPSZMAACUBAAtAg0YERI6c5QABYIEAB0AA44II1+pDC+fpVZOflFJWU4FRkwNXVNLY1hHeE92XkFxaXlPeMNza1xs-Hpps6bbQCEicFmB1NhJzBByecwh3HXtzQmpuaWEFK16DBiImwvrZhg40hdWn5nlEzulDldTnd0rkFOgsLhVDhYVMngjXu8hNBOh0eAB3b4IdDkADkfj8VIEVLCYXpMCpcTiVK05lcIBQSHqKBANB8XIWeEmENIJDIrHYXB4aF6MAA6gAVOAmMUS6ZSsiM5lKgDyAGlNTlxY9dSw2JxuLwlWqNUA

💻 Code

const FieldDecorator = (target: undefined, context: ClassFieldDecoratorContext) => {} // do nothing

class Parent {
  constructor(arg1: string, arg2: string, arg3: string) {
    // @ts-ignore
    this.prop1 = arg1
    // @ts-ignore
    this.prop2 = arg2
    // @ts-ignore
    this.prop3 = arg3
  }
}

class Child extends Parent {
  prop1!: string

  prop2!: string

  @FieldDecorator
  prop3!: string
}

const a = new Child('11', '22', '33')
console.log(a)
// a.prop1 === undefined // WTF
// a.prop2 === '22' // OK
// a.prop3 === undefined // WTF

🙁 Actual behavior

the decorated property and the very first property are undefined despite the fact that they are given a value in the constructor

🙂 Expected behavior

a object should be equal to the following obj object

const obj = {
    prop1: "11"
    prop2: "22"
    prop3: "33"
} 

Additional information about the issue

No response