Object.defineProperty doesn't define properties on 'this'

[DanielRosenwasser]

// @ts-check

class C {
  constructor() {
    Object.defineProperty(this, "x", { value: "hello" });

    this.x.toLowerCase();
  }
}

Expected: No error.
Actual: Property 'x' does not exist on type 'C'.

[xprommer]

Unfortunately it doesn't work in TS as well,
if you run this in TS playground (I guess it has the latest TS version)

let obj = {};
Object.defineProperty(obj, "x", { value: "hello", writable: false });

obj.x.toLowercase();

then it will show only one error message:
"Property 'x' does not exist on type '{}'"

but I expected to get different error like "Property 'toLowercase' does not exist on type 'string'" as was described in https://devblogs.microsoft.com/typescript/announcing-typescript-3-2/#objectdefineproperty-declarations-in-javascript

[tokland]

@DanielRosenwasser See #14650

[DanielRosenwasser]

@tokland This is about JavaScript analysis, not TypeScript.

[boneskull]

I'm running in to this one. Anyone know of a workaround?

[boneskull]

n/m, workaround for above is something like this:

// @ts-check

class C {
  constructor() {
    /** @type {Readonly<string>} */
    this.x = undefined;
    Object.defineProperty(this, "x", { value: "hello" });

    this.x.toLowerCase();
  }
}

[akornatskyy]

You need to add definite assertion assignment to property 'x: string'.

class C {
  x!: string;  // definite assertion
  constructor() {
    Object.defineProperty(this, 'x', {value: 'hello'});
    this.x.toLowerCase();
  }
}

[brainkim]

@akornatskyy I think the source is assumed to be JavaScript in this issue and there is no definite assignment assertion syntax there as far as I can tell.