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evanw / esbuild

An extremely fast bundler for the web
https://esbuild.github.io/
MIT License
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decorators on uninitialized class fields are not working when `useDefineForClassFields: false` #3913

Closed hi-ogawa closed 2 months ago

hi-ogawa commented 2 months ago

Related: https://github.com/evanw/esbuild/issues/3911, https://github.com/vitejs/vite/issues/18105

Full code to compare with tsc is here https://github.com/hi-ogawa/reproductions/tree/main/vite-18105-decorator-useDefineForClassFields

Here is a part of the code on esbuild try

function testDecorator(_value: unknown, context: DecoratorContext) {
    if (context.kind === "field") {
        return () => "dec-ok";
    }
}

class DecClass {
    @testDecorator
    decInit = "init";

    @testDecorator
    decNoInit: any;
}

console.log(new DecClass())
// esbuild: DecClass { decInit: 'dec-ok' }
// tsc:     DecClass { decInit: 'dec-ok', decNoInit: 'dec-ok' }

Vite uses useDefineForClassFields: false for esbuild transform when users don't not explicitly set, but this specific decorator usages being not working seems to lead to a bit surprising behavior.