TypeScript: ECMAScript private method overloading results in syntax error

[davecardwell]

Version

v24.4.1

Platform

Darwin mac.lan 24.5.0 Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:33 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T8122 arm64

Subsystem

No response

What steps will reproduce the bug?

Node.js’ type stripping results in a syntax error when using function overloading with ECMAScript private methods.

class Foo {
 #bar(baz: string): string;
 #bar(baz: number): number;
 #bar(baz: string | number): string | number;
 #bar(baz: string | number): string | number {
 return baz;
 }

 public bar(baz: string | number): string | number {
 return this.#bar(baz);
 }
}


console.log(new Foo().bar(42));

This example is valid TypeScript and compiles as expected under tsc.

How often does it reproduce? Is there a required condition?

Consistently.

What is the expected behavior? Why is that the expected behavior?

I expect the example to run and output 42.

It compiles under the tsc command and the output can be executed with Node.js:

// output of:
// pnpm --package typescript dlx tsc --target es2022 index.ts

class Foo {
 #bar(baz) {
 return baz;
 }
 bar(baz) {
 return this.#bar(baz);
 }
}
console.log(new Foo().bar(42));

What do you see instead?

/private/tmp/foo/index.ts:2
 #bar(baz ) ;
 ^

SyntaxError: Unexpected token ';'
 at wrapSafe (node:internal/modules/cjs/loader:1624:18)
 at Module._compile (node:internal/modules/cjs/loader:1666:20)
 at Object..js (node:internal/modules/cjs/loader:1824:10)
 at Module.load (node:internal/modules/cjs/loader:1427:32)
 at Module._load (node:internal/modules/cjs/loader:1250:12)
 at TracingChannel.traceSync (node:diagnostics_channel:322:14)
 at wrapModuleLoad (node:internal/modules/cjs/loader:235:24)
 at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:152:5)
 at node:internal/main/run_main_module:33:47

Node.js v24.4.1

Additional information

Reported to swc-project/swc#10884.

[dnalborczyk]

looks like a bug in swc:

https://play.swc.rs/?version=1.12.14&code=H4sIAAAAAAAAA0vOSSwuVnDLz1eo5lJQUE5KLNJISqyyUiguKcrMS9eEMaxRJPNKc5NSizRhDGssOhVqEKrQREhUDnaYgkJRaklpUZ4CUA9Ify0XkCgoTcrJTFYg16iSjMxiPZhDNCGmAs3lSs7PK87PSdXLyU%2FXyEstBwWOhqYeSJ2JkaamNQC6mwipMgEAAA%3D%3D&config=H4sIAAAAAAAAA1WOvQ6DMAyE9zwF8sxQMXbryGNE4FahJI5sI4EQ745DS382%2Bz7f%2BVZXVTBIB9dqtdEWnDNyiJjUjx%2FV9CdibmMm1psIsgZKYlx5wuNkq1%2F%2B7Nnwr1MWy5pNAV0ySschK9QnVSno7kf5z1HPD9TiQmkuTQPuzSBSP434bRyOVm1SZMrFkKhHOGPsZdE6ipHSIEeM29wOxse8CvkAAAA%3D&strip-types=

[davecardwell]

Thanks @dnalborczyk. Reported here: swc-project/swc#10884

[marco-ippolito]

Thanks for the report, it should be fixed by updating amaro, I'll write a test to make sure