non-null assertion in typescript changes generated javascript

[hunkydoryrepair]

Describe the bug

Typescript documentation explicitly states that using the non-null assertion (!) does not change the emitted code.

But, using swc, this isn't the case. The following create different outputs:

a?.b!.c ?? 0
vs
a?.b.c ?? 0

At least, when targeting ES5.

The first case will generate something like:

(_a = (a === null || a === void 0 ? void 0 : a.b).x) !== null && _a !== void 0 ? _a : 0

while the second generates

(_a = a === null || a === void 0 ? void 0 : a.b.x) !== null && _a !== void 0 ? _a : 0

Using tsc, these expressions generate the same output.

Works as expected in versions < 1.3.63

Input code

a?.b!.c ?? 0

Config

n/a

Playground link

https://play.swc.rs/?version=1.3.75&code=H4sIAAAAAAAAA0u010tS1EtWsLdXMAAAPu9sgQwAAAA%3D&config=H4sIAAAAAAAAA1WPSw7CMAxE9z1F5DVbWHAHDmEFtwrKT7GRiKrenaRJCt3ZM2M%2Fe52UghdruKu1lKWJmJjS0ReFsxf8FAUkR2KdTBS4DFe4WjNapl3amgOCaSGpU8TXHgcbAtOId80Zb%2Bb8D9TBxUTM52CNol8snXFTR4ILz%2Fdu9kfqsQ1%2Fg19owI7FYPgxJtva7QvTya0RFQEAAA%3D%3D

Expected behavior

a?.b.c runs identically to a?.b!.c

output
(_a = a === null || a === void 0 ? void 0 : a.b.x) !== null && _a !== void 0 ? _a : 0

Actual behavior

Using a?.b!.c throws an error at runtime when a is undefined, while a?.b.c does not.

outputs
(_a = (a === null || a === void 0 ? void 0 : a.b).x) !== null && _a !== void 0 ? _a : 0

Version

1.3.63 - 1.3.75

Additional context

No response

[magic-akari]

This issue will be fixed in #7202

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.