microsoft / microsoft/TypeScript

Incorrect class #private fields initialization order with target ES2022 and useDefineForClassFields set to false

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Since May 10, 2023.

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Description

Bug Report

🔎 Search Terms

ES2022 class field initialization order
private fields order
useDefineForClassFields false

🕗 Version & Regression Information
  • This changed between versions 4.9.5 and 5.0.4
⏯ Playground Link

5.0.4 with runtime error (useDefineForClassFields: false, target: ES2022)

4.9.5 without runtime error (useDefineForClassFields: false, target: ES2022)

💻 Code
class Buzz {
    wow = 'one'
}

class Foo { 
    #bar = this.buz.wow;
    constructor(private buz: Buzz) {}
}

new Foo(new Buzz())
🙁 Actual behavior

With 5.0.4 and useDefineForClassFields: false, target: ES2022 the above code fails in runtime because #bar = this.buz.wow; stays initialized before constructor, this doesn't happen if "normal private" is used (private bar = this.buz.wow;). Such construct works without issues on 4.9.5.

🙂 Expected behavior

The initialization is done in the same way as on 4.9.5.

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