Bug Report

🔎 Search Terms

useDefineForClassFields

🕗 Version & Regression Information

• This changed sometime between versions 3.7 and 4.2.4
• Upgrading the version of Typescript in Visual Studio 2019 introduced this issue

⏯ Playground Link

Same code compiles in VS Code and command lines, it breaks in Visual Studio 2019+Typescript 4.2.4 only

💻 Code

Use a @decorator on class properties or any code that is incompatible with useDefineForClassFields: true

Something like:

class MyClass {
    @myDecorator()
    myField: any;
}

Do not include useDefineForClassFields in your tsconfig.json at all.

Run Typescript compile.

When VS2019 with TS 4.2.4 compiles JS output includes class fields, something like:

var __decorate = // ...autogenerated implementation

let MyClass = class MyClass {
    myField;
};

__decorate([
    myDecorator()
], MyClass.prototype, "myField", null);

When tsc 4.3.5 compiles for the same tsconfig and source files it doesn't include class fields, something like:

var __decorate = // ...autogenerated implementation

let MyClass = class MyClass {
    // No fields here
};

__decorate([
    myDecorator()
], MyClass.prototype, "myField", null);

Adding useDefineForClassFields: false works around the issue and makes the JS output consistent.

Property decorators are ignored (as per #35081).

🙁 Actual behaviour

JS output includes class fields (as if useDefineForClassFields was set to true) in VS2019+TS 4.2.4
JS output does not include class fields (as if useDefineForClassFields was set to false) in tsc 3.7 or 4.3

🙂 Expected behaviour

JS output should not include class fields unless useDefineForClassFields is explicitly set to true.

Whatever default useDefineForClassFields setting is should be consistent between tsc and VS2019+TS