swc-project / swc-project/swc-node

Object.assign not working properly

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TypeScript
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Description

@swc-node/jest behaves differently with jest 27.5.1.
As of yesterday when I updated jest, I'm getting some weird behavior from swc-node that is causing most of my unit tests to break. Object.assign is no longer working properly with this library.

The exact thing that is newly failing is the following (simplified for example):

export class Base<T> {
  constructor(props: Partial<T> = {}) {
    Object.assign(this, props);
  }
}

export class SomeClass extends Base<SomeClass> {
  a: string;
  b: boolean;
  c: number;
  d: string;
}

Expected:

const test = new SomeClass({ a: 'hello', b: false })
// test -> { a: 'hello', b: 'false' }

Actual:

const test = new SomeClass({ a: 'hello', b: false })
// test -> { a: undefined, b: undefined, c: undefined, d: undefined }

Note that our code works fine with ts-jest while using the new jest version.

NPM Version: 8.3.2
Node Version: 16.10.0
@swc-node/core version: 1.8.2
@swc-node/jest version: 1.4.3
jest version: 27.5.1

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the supplied TypeScript example through @swc-node/jest with Jest 27.5.1, using the reported Node, @swc-node/core, and @swc-node/jest versions. Compare the behavior with ts-jest and inspect the @swc-node/jest integration to identify why Object.assign produces undefined fields; done means the example behaves correctly under the reported Jest version.

Written by the indexing model from the issue text.

Assessment

Tech stack
node.js, typescript
Domain
testing-qa, tooling
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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