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fix: preserve invalid Date instead of dropping it to null #355

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fix: preserve invalid Date instead of dropping it to null #355

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19 changes: 19 additions & 0 deletions src/index.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,25 @@ describe('stringify & parse', () => {
},
},

'works for invalid dates': {
input: {
date: new Date('invalid'),
},
output: {
date: '',

@Skn0tt Skn0tt Jun 29, 2026

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let's use Invalid Date as the sentinel value instead of ''.

},
outputAnnotations: {
values: {
date: ['Date'],
},
},
dontExpectEquality: true,
customExpectations: value => {
expect(value.date).toBeInstanceOf(Date);
expect(Number.isNaN(value.date.getTime())).toBe(true);
},
},

'works for Errors': {
input: {
e: new Error('epic fail'),
Expand Down
8 changes: 5 additions & 3 deletions src/transformer.ts
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
import {
isBigint,
isDate,
isInfinite,
isMap,
isNaNValue,
Expand Down Expand Up @@ -73,9 +72,12 @@ const simpleRules = [
}
),
simpleTransformation(
isDate,
(v): v is Date => v instanceof Date,
'Date',
v => v.toISOString(),
// An invalid Date (`new Date(NaN)`) has no ISO representation and would
// otherwise be dropped to `null`, losing its type. Serialize it to an
// empty string, which `new Date('')` revives back into an invalid Date.
v => (isNaN(v.valueOf()) ? '' : v.toISOString()),
v => new Date(v)
),

Expand Down