Static property access fails in transpiled JS code when referenced in a private method in TypeScript 5.2.2

[treblasft]

🔎 Search Terms

static property access private method transpiled JS

🕗 Version & Regression Information

• This changed between versions 5.1.6 and 5.2.2 [using Target: ES2022, Module: Node16]

⏯ Playground Link

https://www.typescriptlang.org/play?target=9&moduleResolution=99&module=100&ts=5.2.2&noUnusedLocals=true&jsx=4&pretty=true&preserveWatchOutput=false&noErrorTruncation=true&isolatedModules=true&verbatimModuleSyntax=true&inlineSourceMap=true#code/KYDwDg9gTgLgBAYwDYEMDOa4EE4G8BQccaMKMAlgnGFBGDgLxwDkAdigLbDMDchxpClRp0AQnCZYAdCPp8iAegVEVqtXAB6WrXAAqATzDAAolFpQAXHADCKVqwjwowFABNqtI7HLBMEAGZwAK6srsD+5KzA7gAUzm6RAOYssljMAJT4-EpwALIoANZJcDAAFuSYXGUQ7mBBAEZIlHAchb4lUHZoYORI0XAAUgDKiDXAcADu0AVw6HCgRggw0fwAxEFgrmTAAKpowFAx6Xj8RM4wQVCs2DKeWPJwAL74z0A

💻 Code

After updating to TypeScript 5.2.2, I encountered a TypeError when trying to access a static property on the same class. The compiled JavaScript code results in a reference to an uninitialized variable. This error seems to occur when a static member is referenced in a private method in the class.

export class A {
    static propA = 'name';
    static propB = A.propA;
    //               ^^^^^ (At runtime) TypeError: Cannot read properties of undefined (reading 'propA')

    // Making this method public makes transpiled JavaScript code work as expected
    #updateUser() {
        return A.propA;
    }
}

🙁 Actual behavior

The transpiled JavaScript results in a TypeError due to _a being used before it is assigned a value. The transpilation output incorrectly references _a instead of A in the static property initialization and inside the private method.

var _a;
export class A {
    static propA = 'name';
    static propB = _a.propA;
    //                ^^^^^ TypeError: Cannot read properties of undefined (reading 'propA')

    #updateUser() {
        return _a.propA; // The culprit seems to be this line
    }
}
_a = A; // _a is defined too late

🙂 Expected behavior

The static properties should be accessed the same way it does in the TypeScript code, as it is completely correct JavaScript code.

export class A {
    static propA = 'name';
    static propB = A.propA; // The static member is referenced as expected

    #updateUser() {
        return A.propA;
    }
}

Additional information about the issue

Making the #updateUser method public makes TypeScript transpile JavaScript code as expected.

[jcalz]

It's not a crash if it successfully emits JavaScript. "Crash" means that tsc crashes. (I wish the issue template would make this more clear)

[treblasft]

Thanks for the clarification, Joe Calzaretta (@jcalz). Updated the issue description!

[savitakatwe]

Albert Mañosa (@treblasft)
`class A {
static propA = 'name';
static propB: string;

constructor(){
A.propB = A.propA
}

// Making this method public makes transpiled JS code work as expected
updateUser() {
return A.propA;
}
}`
you might consider initializing static propB within the constructor after the class declaration.

[trusktr]

consider initializing static propB within the constructor after the class declaration.

Another workaround is to use this instead of A and then you also get inheritance:

export class A {
  static propA = 'name';
  static propB = this.propA;

  // Making this method public makes transpiled JS code work as expected
  #updateUser() {
    return A.propA; // also consider using `this.constructor.propA` for inheritance, but it needs casting until https://github.com/microsoft/TypeScript/issues/3841 is fixed
  }
}