JavaScript Date.parse: Use Explicit ISO Instants and Check Failure

The task

Compare two spellings of the same instant, reject an unmistakably invalid string and inspect a date-only input separately. Avoid relying on the host’s local time zone.

Runnable Node 22 example

const assert = require('node:assert/strict');

const utc = Date.parse('2026-10-20T09:00:00Z');
const offset = Date.parse('2026-10-20T11:00:00+02:00');
assert.equal(utc, offset);
assert.equal(new Date(utc).toISOString(), '2026-10-20T09:00:00.000Z');
assert.equal(Number.isNaN(Date.parse('not-a-date')), true);
const dateOnly = Date.parse('2026-10-20');
assert.equal(new Date(dateOnly).toISOString(), '2026-10-20T00:00:00.000Z');
console.log(new Date(utc).toISOString());
console.log(new Date(dateOnly).toISOString());

Expected output and explanation

The +02:00 spelling is two hours ahead of UTC on its displayed clock, so eleven there equals nine UTC. Both parse to the same instant. The invalid text returns NaN, which should be checked before formatting or subtracting timestamps.

The date-only form in this supported grammar is interpreted as UTC midnight. That is not proof that the user intended midnight in their local zone. An appointment date and an instant are different data requirements; choose a representation and zone policy that reflects the task.

Pitfall to check

Date.parse is not a comprehensive calendar-field validator. Some out-of-range-looking inputs can normalize or vary outside the supported format. Validate required date components deliberately rather than using one successful parse as proof of every business rule.