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Add example of pure ownPropertyNames typing #94

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Add example of pure ownPropertyNames typing #94

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27 changes: 27 additions & 0 deletions tests/iterable/ownPropertyNames.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -36,4 +36,31 @@ describe('ownPropertyNames', () => {
const result = Array.from(_.ownPropertyNames(new TestClass()))
expect(result).toEqual(['a'])
})
test("don't provide unexpected properties after type narrowing", () => {
type FullLog = 'debug' | 'info' | 'error' | 'warn'
type ProdLog = Extract<FullLog, 'warn' | 'error'>

const error = vi.fn()
const warn = vi.fn()

const handlers = { error, warn }

function handleLogs(logs: { [key in ProdLog]: number }) {
for (const log of _.ownPropertyNames(logs)) {
handlers[log]()
}
}

const logs: { [key in FullLog]: number } = {
error: 1,
warn: 2,
info: 3,
debug: 4,
}

handleLogs(logs)

expect(error).toHaveBeenCalledTimes(1)
expect(warn).toHaveBeenCalledTimes(1)
})
})