TS2565 false positive in JS for a class field initialized in the base class

[harshmandan]

🔎 Search Terms

TS2565, used before being assigned, checkJs, class field, extends

🕗 Version & Regression Information

• Fails: 7.0.2, 7.1.0-dev.20260928.1
• Works: @typescript/native-preview@7.0.0-dev.20260417.1, TypeScript 5.x/6.x
• Possibly from Port CFA for expando property access expressions typescript-go#4177 (fix for tsgo does not report TS2565 for conditionally-assigned expando function properties typescript-go#4134)

💻 Code

src/product.js with allowJs, checkJs, strict:

export class BaseProduct {
  Price = 0
}

export class Product extends BaseProduct {
  Compute() {
    this.Price = Number(this.Price);
  }
}

🙁 Actual behavior

src/product.js(7,30): error TS2565: Property 'Price' is used before being assigned.

🙂 Expected behavior

No error. Price is initialized in the base class. The same code in a .ts file has no error.

[jwbth]

Same with the base property assigned in the constructor rather than as a class field:

class Base {
  constructor() {
    /** @type {HTMLElement} */
    this.element = document.createElement('div')
  }
}

class Derived extends Base {
  replace() {
    this.element.replaceWith(document.body) // TS2565
    this.element = document.body
  }
}

Reading through destructuring (const { element } = this) avoids it.