`format()` fails with "Invalid offset format" on Microsoft Edge 32-bit (Chromium)

[Infern1]

Description

The format() function throws Error: Invalid offset format on Microsoft Edge 32-bit (Chromium-based, version 144.0.3719.82). The same code works perfectly on Edge 64-bit.

Root Cause

Edge 32-bit has a bug in Intl.DateTimeFormat.formatToParts() where time components are silently dropped when:

1. A non-UTC timezone is specified (e.g., timeZone: 'Europe/Berlin')
2. AND time options use '2-digit' format

This causes tempo's offset() function (in offset.mjs) to receive incomplete date parts, resulting in an invalid Date object and ultimately NaN values in the offset calculation.

Reproduction

// This works on Edge 64-bit but FAILS on Edge 32-bit
import { format } from '@formkit/tempo';

const date = new Date('2026-01-20T08:07:40.000Z');
const result = format(date, 'YYYY-MM-DD HH:mm:ss');
// Edge 32-bit throws: Error: Invalid offset format

Debug Information

Edge 32-bit behavior with Intl.DateTimeFormat:

// Using '2-digit' - BROKEN on Edge 32-bit
const formatter = new Intl.DateTimeFormat('en-US', {
  timeZone: 'Europe/Berlin',
  year: 'numeric', month: '2-digit', day: '2-digit',
  hour: '2-digit', minute: '2-digit', second: '2-digit',
  hourCycle: 'h23'
});
console.log(formatter.formatToParts(new Date()));

// Output on Edge 32-bit (TIME PARTS MISSING!):
[
  { "type": "month", "value": "01" },
  { "type": "literal", "value": "/" },
  { "type": "day", "value": "20" },
  { "type": "literal", "value": "/" },
  { "type": "year", "value": "2026" }
]

// Using 'numeric' - WORKS on Edge 32-bit
const formatter2 = new Intl.DateTimeFormat('en-US', {
  timeZone: 'Europe/Berlin',
  year: 'numeric', month: '2-digit', day: '2-digit',
  hour: 'numeric', minute: 'numeric', second: 'numeric'
});
console.log(formatter2.formatToParts(new Date()));

// Output on Edge 32-bit (correct):
[
  { "type": "month", "value": "01" },
  { "type": "literal", "value": "/" },
  { "type": "day", "value": "20" },
  { "type": "literal", "value": "/" },
  { "type": "year", "value": "2026" },
  { "type": "literal", "value": ", " },
  { "type": "hour", "value": "10" },
  { "type": "literal", "value": ":" },
  { "type": "minute", "value": "47" },
  { "type": "literal", "value": ":" },
  { "type": "second", "value": "30" },
  { "type": "literal", "value": " " },
  { "type": "dayPeriod", "value": "AM" }
]

How tempo fails

1. format() calls offset(inputDate, tz, "utc") in format.mjs:30
2. offset() uses relativeTime() which calls Intl.DateTimeFormat(...).formatToParts()
3. On Edge 32-bit, formatToParts() returns only date parts (no hour/minute/second)
4. relativeTime() constructs: "2026-01-20T${undefined}:${undefined}:${undefined}Z"
5. new Date(...) returns Invalid Date
6. getTime() returns NaN
7. secsToOffset(NaN) produces "+NaN:NaN:NaN"
8. fixedLengthByOffset("+NaN:NaN:NaN") throws "Invalid offset format"

Environment

• Browser: Microsoft Edge 144.0.3719.82 (Official build) (32-bit) - Chromium-based
• OS: Windows
• @formkit/tempo version: 1.0.0

Suggested Fix

Option 1: Add try/catch in format() with graceful degradation

Option 2: In offset.mjs, validate that relativeTime() returns a valid Date before calculating offset

Option 3: Consider using 'numeric' instead of '2-digit' for internal Intl.DateTimeFormat options (though this may affect output formatting)

Workaround

We've implemented a wrapper that catches the error and falls back to native Date formatting:

import { format as tempoFormat } from '@formkit/tempo';

export function format(date, formatStr) {
  try {
    return tempoFormat(date, formatStr);
  } catch {
    // Native fallback for Edge 32-bit
    const pad = (n) => n.toString().padStart(2, '0');
    return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())} ${pad(date.getHours())}:${pad(date.getMinutes())}:${pad(date.getSeconds())}`;
  }
}

Related

This is a Chromium/Edge bug that should also be reported to Microsoft, but tempo could be more resilient to malformed Intl responses.