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Svelte 5: TS property type annotations are not fully erased #12685

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brunnerh opened this issue Aug 1, 2024 · 3 comments
Closed

Svelte 5: TS property type annotations are not fully erased #12685

brunnerh opened this issue Aug 1, 2024 · 3 comments

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@brunnerh
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brunnerh commented Aug 1, 2024

Describe the bug

If a property is only typed and not assigned, it should be removed from output, otherwise there can be issues with shadowing.

Reproduction

<script lang="ts">
	class AutoAssign<T> {
			constructor(props: T) {
					Object.assign(this, props);
			}
	}

	class Test extends AutoAssign<Test> {
			id!: string; // remove this to make it work
	}

	const test = new Test({ id: 'test' });
	console.log('ID', test.id);
</script>

test: {JSON.stringify(test)}

REPL

Class after Svelte strips the types:

class Test extends AutoAssign {
	id; // remove this to make it work
}

In TS playground

(vitePreprocess and sveltePreprocess seem to remove the properties.)

Logs

No response

System Info

REPL

Severity

annoyance
@dummdidumm
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I vaguely remember TS saying that this may be the right behavior because of how classes work now, and if you use some new option to downlevel classes differently it's the same output - but I could be mistaken

@jasonlyu123
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The new option is useDefineForClassFields and it's the default if target is ES2022 or higher.

https://www.typescriptlang.org/play/?useDefineForClassFields=true&target=9#code/MYGwhgzhAECCCuAXA9rKBLA5gOwDwBUA aAbwCgBIC4ZbCRAJ3mBQYAoAHB5DiALmj4AlKUpUKAeQBGAKwCmLAHSQIWbG0QALdBAA00LjwhCA3GIC ZS2VArBc tDkAPRHOwATGAhRpVOAgdEYnIqdA8AQgF6BnRsTBNoAHok6AY5AFtkADc5aC0dfORoDLAAazz0RGgAd2QGMqsyG1pHN0cAXmhsORr7ejYSaHCBAHJ2xFHoc1MWumQQOUUQZEw2UYBJABFR-QnFcNMgA

@brunnerh
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brunnerh commented Aug 1, 2024

I tested changing the target/useDefineForClassFields and the behavior appears to conform to the configuration.
So I would call that user error (though those TS flags can be a bit tricky).

@brunnerh brunnerh closed this as not planned Won't fix, can't repro, duplicate, stale Aug 1, 2024
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3 participants
@brunnerh @dummdidumm @jasonlyu123