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Jimbly merged 2 commits into from
Feb 17, 2026
Merged

Accommodate insane behavior of Date.UTC #81

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0ac5c2d
Accommodate insane behavior of Date.UTC
dmurvihill Feb 14, 2026
2beafb5
Improve tests
dmurvihill Feb 17, 2026
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4 changes: 3 additions & 1 deletion index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -210,7 +210,9 @@ MockDate.prototype.fromLocal = function () {
offsets.reduce(function (acc, o) {
var bestTs = acc[0];
var correctOffset = acc[1];
var ts = _Date.UTC.apply(null, localComponents) - (o * HOUR);
var ts = new _Date(
_Date.UTC.apply(null, localComponents)
).setUTCFullYear(localComponents[0]) - (o * HOUR);
if (-mockDate.calcTZO(ts) === o) {
return [correctOffset === false || ts < bestTs ? ts : bestTs, true];
}
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5 changes: 3 additions & 2 deletions package-lock.json
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67 changes: 39 additions & 28 deletions tests/test-setters.js
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Expand Up @@ -194,59 +194,70 @@ testIssue78()

// Format: mock tz, local time at start, argument to setDate(), expected absolute time at end
const cases = [
['US/Eastern', '2025-01-11T12:00:00', 12, '2025-01-12T12:00:00-05:00'], // set forward by one day, nothing funny
['US/Eastern', '2025-01-11T12:00:00', 10, '2025-01-10T12:00:00-05:00'], // set backward by one day
['US/Eastern', '2025-01-11T01:00:00', 12, '2025-01-12T01:00:00-05:00'], // mock/real split across a day boundary
['US/Eastern', '2025-01-11T01:00:00', 10, '2025-01-10T01:00:00-05:00'], // same, but set the day backward
['US/Eastern', '2025-03-07T12:00:00', 11, '2025-03-11T12:00:00-04:00'], // Clock changes forward
['US/Eastern', '2025-03-11T12:00:00', 7, '2025-03-07T12:00:00-05:00'], // Clock un-changes forward
['US/Eastern', '2025-11-01T12:00:00', 3, '2025-11-03T12:00:00-05:00'], // Clock changes backward
['US/Eastern', '2025-11-03T12:00:00', 1, '2025-11-01T12:00:00-04:00'], // Clock un-changes backward
['US/Eastern', '2025-01-11T12:00:00', 'setDate', 12, '2025-01-12T12:00:00-05:00'], // set forward by one day, nothing funny
['US/Eastern', '2025-01-11T12:00:00', 'setDate', 10, '2025-01-10T12:00:00-05:00'], // set backward by one day
['US/Eastern', '2025-01-11T01:00:00', 'setDate', 12, '2025-01-12T01:00:00-05:00'], // mock/real split across a day boundary
['US/Eastern', '2025-01-11T01:00:00', 'setDate', 10, '2025-01-10T01:00:00-05:00'], // same, but set the day backward
['US/Eastern', '2025-03-07T12:00:00', 'setDate', 11, '2025-03-11T12:00:00-04:00'], // Clock changes forward
['US/Eastern', '2025-03-11T12:00:00', 'setDate', 7, '2025-03-07T12:00:00-05:00'], // Clock un-changes forward
['US/Eastern', '2025-11-01T12:00:00', 'setDate', 3, '2025-11-03T12:00:00-05:00'], // Clock changes backward
['US/Eastern', '2025-11-03T12:00:00', 'setDate', 1, '2025-11-01T12:00:00-04:00'], // Clock un-changes backward

// One offset changes, but the other offset doesn't
['US/Eastern', '2025-03-08T03:30:00', 9, '2025-03-09T03:30:00-04:00'], // ET changes forward, PT doesn't
['US/Eastern', '2025-03-10T03:30:00', 9, '2025-03-09T03:30:00-04:00'], // PT un-changes forward, ET doesn't
['US/Eastern', '2025-11-03T02:30:00', 2, '2025-11-02T02:30:00-05:00'], // PT un-changes backward, ET doesn't
['US/Eastern', '2025-03-08T03:30:00', 'setDate', 9, '2025-03-09T03:30:00-04:00'], // ET changes forward, PT doesn't
['US/Eastern', '2025-03-10T03:30:00', 'setDate', 9, '2025-03-09T03:30:00-04:00'], // PT un-changes forward, ET doesn't
['US/Eastern', '2025-11-03T02:30:00', 'setDate', 2, '2025-11-02T02:30:00-05:00'], // PT un-changes backward, ET doesn't
// Also, this starting time splits real and mock across a day boundary (02:30 EDT / 23:30 PDT)
['US/Eastern', '2025-11-01T02:30:00', 2, '2025-11-02T02:30:00-05:00'], // ET changes backward, PT doesn't
['US/Eastern', '2025-11-01T02:30:00', 'setDate', 2, '2025-11-02T02:30:00-05:00'], // ET changes backward, PT doesn't

['America/Anchorage', '2025-01-11T12:00:00', 12, '2025-01-12T12:00:00-09:00'], // set forward by one day, nothing funny
['America/Anchorage', '2025-01-11T12:00:00', 10, '2025-01-10T12:00:00-09:00'], // set backward by one day
['America/Anchorage', '2025-01-11T23:30:00', 11, '2025-01-11T23:30:00-09:00'], // mock/real split across a day boundary
['America/Anchorage', '2025-01-11T23:30:00', 12, '2025-01-12T23:30:00-09:00'], // same, but set the day forward
['America/Anchorage', '2025-03-07T12:00:00', 11, '2025-03-11T12:00:00-08:00'], // Clock changes forward
['America/Anchorage', '2025-03-11T12:00:00', 7, '2025-03-07T12:00:00-09:00'], // Clock un-changes forward
['America/Anchorage', '2025-11-01T12:00:00', 3, '2025-11-03T12:00:00-09:00'], // Clock changes backward
['America/Anchorage', '2025-11-03T12:00:00', 1, '2025-11-01T12:00:00-08:00'], // Clock un-changes backward
['America/Anchorage', '2025-01-11T12:00:00', 'setDate', 12, '2025-01-12T12:00:00-09:00'], // set forward by one day, nothing funny
['America/Anchorage', '2025-01-11T12:00:00', 'setDate', 10, '2025-01-10T12:00:00-09:00'], // set backward by one day
['America/Anchorage', '2025-01-11T23:30:00', 'setDate', 11, '2025-01-11T23:30:00-09:00'], // mock/real split across a day boundary
['America/Anchorage', '2025-01-11T23:30:00', 'setDate', 12, '2025-01-12T23:30:00-09:00'], // same, but set the day forward
['America/Anchorage', '2025-03-07T12:00:00', 'setDate', 11, '2025-03-11T12:00:00-08:00'], // Clock changes forward
['America/Anchorage', '2025-03-11T12:00:00', 'setDate', 7, '2025-03-07T12:00:00-09:00'], // Clock un-changes forward
['America/Anchorage', '2025-11-01T12:00:00', 'setDate', 3, '2025-11-03T12:00:00-09:00'], // Clock changes backward
['America/Anchorage', '2025-11-03T12:00:00', 'setDate', 1, '2025-11-01T12:00:00-08:00'], // Clock un-changes backward

// One offset changes, but the other offset doesn't
['America/Anchorage', '2025-03-08T01:30:00', 9, '2025-03-09T01:30:00-09:00'], // PT changes forward, AKT doesn't
['America/Anchorage', '2025-03-10T01:30:00', 9, '2025-03-09T01:30:00-09:00'], // AKT un-changes forward, PT doesn't
['America/Anchorage', '2025-03-08T01:30:00', 'setDate', 9, '2025-03-09T01:30:00-09:00'], // PT changes forward, AKT doesn't
['America/Anchorage', '2025-03-10T01:30:00', 'setDate', 9, '2025-03-09T01:30:00-09:00'], // AKT un-changes forward, PT doesn't

// Cannot test split PT/AKT transitions, because the interval between the
// PT and AKT transition is shorter than the magnitude of the transition itself.
// AKT is the most negative zone that observes DST, so there's no way
// to exercise this case as long as the tests run in US/Pacific.
// ['America/Anchorage', '2025-11-03T??:??:??', 2, '2025-11-02T??:??:??-08:00'], // AKT un-changes backward, PT doesn't
// ['America/Anchorage', '2025-11-03T??:??:??', 'setDate', 2, '2025-11-02T??:??:??-08:00'], // AKT un-changes backward, PT doesn't

// Can't cross a day boundary with this test; need at least 3 hours of relative offset
// ['America/Anchorage', '2025-11-01T00:59:00', 2, '2025-11-02T01:59:00-08:00'], // PT changes backward, AKT doesn't
// ['America/Anchorage', '2025-11-01T00:59:00', 'setDate', 2, '2025-11-02T01:59:00-08:00'], // PT changes backward, AKT doesn't

// setFullYear
['US/Eastern', '2015-12-31T19:30:00-05:00', 'setFullYear', 2015, '2015-12-31T19:30:00-05:00'], // Mock and UTC in different years
['US/Eastern', '2015-12-31T19:30:00-05:00', 'setFullYear', 2016, '2016-12-31T19:30:00-05:00'],
['US/Eastern', '2015-01-01T00:30:00-05:00', 'setFullYear', 2015, '2015-01-01T00:30:00-05:00'], // System and Mock in different years
['US/Eastern', '2015-01-01T00:30:00-05:00', 'setFullYear', 2016, '2016-01-01T00:30:00-05:00'],

// For very old dates, Node uses mean solar time in Los Angeles
// rather than US standard times. timezone_mock does not emulate this,
// so we are expecting to be off by 422 seconds here.
['US/Pacific', '1970-01-01T00:00:00Z' , 'setFullYear', 20, -61504445222000 + 422000 ]
];

for (const c of cases) {
testLocalSetterCase(...c);
}

function testLocalSetterCase(mockTz, startingLocal, newDate, expectedEnd) {
function testLocalSetterCase(mockTz, start, fn, newValue, expectedEnd) {
timezone_mock.register(mockTz)
const d = new Date(startingLocal);
const d = new Date(start);
const t = new timezone_mock._Date(expectedEnd).getTime();
try {
assert.equal(d.setDate(newDate), t)
assert.equal(d[fn](newValue), t)
assert.equal(d.getTime(), t)
} catch (e) {
console.log(JSON.stringify({
mockTz, startingLocal, newDate,
mockTz, start: start, newDate: newValue,
expectedEnd: new Date(expectedEnd).toISOString(),
actualEnd: d.toISOString(),
}, null, 2))
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