Format specifies don't seem to be fully implemented #2582

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1. alfonsogarciacaro commented on Jan 7, 2022

   

   alfonsogarciacaro

   on Jan 7, 2022

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   Supporting all format specifiers is quite complicated and we're doing it bit by bit 😸 You can check which formats are supported in the String tests. In one of the latest releases we added support for thousand separators with the #,## pattern:

   Fable/tests/Main/StringTests.fs

   Lines 352 to 360 in b897166

   	testCase "String.Format works with thousands separator" <| fun () ->
   	(12343235354.6547757).ToString() |> equal "12343235354.654776"
   	(12343235354.6547757).ToString("#,##.000") |> equal "12,343,235,354.655"
   	(12343235354.6547757M).ToString("#,##.000") |> equal "12,343,235,354.655"
   	(123.456).ToString("#,##.00") |> equal "123.46"
   	(123.456M).ToString("#,##.00") |> equal "123.46"
   	(123438192123.456M).ToString("#,##.00") |> equal "123,438,192,123.46"
   	(1.456M).ToString("#,##") |> equal "1"
   	(1.456M).ToString("0,0") |> equal "01"

   If you need something in particular, could you please provide a test like the linked one with the expected results in .NET. Thank you very much!
2. github-actions

   added

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   on Mar 15, 2026
3. github-actions

   added a commit that references this issue on Mar 19, 2026

   Fix N format specifier producing trailing dot when precision is 0

   ...

   This issue will close once commit 885c730 is merged into the 'main' branch.

   885c730
4. github-actions commented on Mar 19, 2026

   

   github-actionsBot

   on Mar 19, 2026 – with GitHub Actions

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   🤖 This is an automated response from Repo Assist.

   Thanks for the report! I investigated the current status of the N format specifier and found that it has been partially fixed over time, but there's still a bug for the N0 case.

   Current status:

   • N / N2 (default precision 2): Works correctly — (1000).ToString("N2") → "1,000.00" ✓
   • N0 (zero decimal places): Broken — (1000).ToString("N0") → "1,000." (trailing dot instead of "1,000")

   Root cause in src/fable-library-ts/String.ts: the N format case unconditionally appends "." + decimal, even when precision = 0. The F format has the correct pattern (guards with if (precision > 0)), but N was missing this guard.

   I've submitted a fix in PR #4422 (if not yet visible, check the linked branch) that mirrors the F format's approach:

   if (precision > 0) {
     rep = thousandSeparate(parts.integral) + "." + padRight(parts.decimal, precision, "0");
   } else {
     rep = thousandSeparate(parts.integral);
   }

   Note: the same trailing-dot bug exists for P0 (percentage) and C0 (currency) format specifiers — those could be fixed in a follow-up PR if needed.

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5. MangelMaxime

   added a commit that references this issue on Mar 25, 2026

   Fix N format specifier producing trailing dot when precision is 0

   ...

   This issue will close once commit 995d251 is merged into the 'main' branch.

   995d251
6. MangelMaxime

   closed this as completedin #4422on Mar 25, 2026
7. github-actions

   added a commit that references this issue on Mar 26, 2026

   Add regression tests for N0, C0, P0 format specifiers

   ...

   665530e