Inheritance Issue with SWC Compilation

[y1j2x34]

Describe the bug

I am currently facing an issue while upgrading an old project to use SWC for compilation. The project consists of both JavaScript and TypeScript files, and there is a scenario where a TypeScript class (New.ts) extends a JavaScript class (Old.js). The TypeScript class includes a private property value, but during SWC compilation, this property is transformed into _define_property._(_assert_this_initialized._(_this), "value", void 0);, leading to value being overwritten as undefined.

Input code

// file: Old.js
class Old {
    constructor() {
        this.value = 123;
    }
}

// file:  New.ts
class New extends Old{
    private value!: number;
}

Config

{
  "jsc": {
    "parser": {
      "syntax": "typescript",
      "tsx": false
    },
    "target": "es5",
    "externalHelpers": true,
    "minify": {
      "compress": false,
      "mangle": false
    },
    "keepClassNames": true,
    "loose": false
  },
  "minify": false,
  "isModule": true,
  "module": {
    "type": "umd"
  }
}

Playground link (or link to the minimal reproduction)

https://play.swc.rs/?version=1.3.107&code=H4sIAAAAAAAAAzXMQQ7CIBQE0P0%2FxbjTDUTdtfEKegak34hBauDTNmm4uy3a2c1M8rTGw3lucPOdeiWy3qS0FsyEJbYPSWK20sf94b%2BtkadLajA%2BMy44ns5tfQoVIr2RuPKoZDOXAp6EQ1f9H%2FWJbjDCqNKuQcjvO8eWyhfiG7IxmAAAAA%3D%3D&config=H4sIAAAAAAAAA22Quw6DMAxFd74Cee7apWuXLu0%2FWGBQ2rxkGwmE%2BPcmlFBUdYvvyc1RPFd1DU9p4FLP6ZiGiCzE%2B5wSmbzimBLQKZI0bKLCqVCVjDq0Qmu0fAgock%2BaWyTn7TrQqMQe7Y1sJJZElQfaoDPedNPR3AQXmUSKYJc69L2lv94XUbxaFHmgox%2BDDUGOrbXz9e4OMHIP7bAaSh1cSbZF5WXk7w2uhfxWtbwBcTGuOk0BAAA%3D

SWC Info output

No response

Expected behavior

We expect that when inheriting properties from a parent class, the initialization and access of those properties should remain intact during SWC compilation.

Actual behavior

No response

Version

1.3.107

Additional context

No response

[kdy1]

See #7435

Class fields are undefined

• Inconsistent useDefineForClassFields behavior #6985
• https://swc.rs/docs/migrating-from-tsc#usedefineforclassfields

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.