Add GetAmountConvertToUnit definitions to both ECMA-262 and ECMA-402 by eemeli · Pull Request #110 · tc39/proposal-amount

eemeli · 2026-05-16T22:12:50Z

Fixes #109 by adding an AO to ECMA-262 that's superseded by a redefinition in ECMA-402.

~~The actual extraction of preferred units from the CLDR units.xml is left as a TODO.~~ Edit: now included.

The preferences depend on unit category, usage, region, and value thresholds. The categories we get from validity/unit.xml, the region is calculated from the first-choice locale, and the preferences themselves are in supplemental/units.xml.

As the data always includes 001 ("the world") as one of the regions for each supported category + usage combination, no locale fallback is ever done during .convertTo(), as all well-formed locales are supported.

github-actions · 2026-05-16T22:13:15Z

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jessealama · 2026-05-18T03:15:32Z

This looks good. Thanks!

gibson042

Thanks! I have many suggestions, but this is an excellent starting point.

gibson042

I'd like to name the Records that are passed between operations, but won't insist on it being part of this PR. The rest of this review is a large handful of non-blocking suggestions.

…ad of locale

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

… options

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Rename two leftover uses of _matchingElements_ to _matchingUnits_, declare GetPreferredUnits as returning a List of Records now that it can no longer throw, drop the ? at its call site accordingly, and add the missing closing asterisk in *"001"*.

Options should be read in alphabetical order (see #95 and review feedback on #110), and alphabetically "locale" precedes "usage".

This reverts the ordering introduced in 5e2ef52. Rejecting incoherent options (no unit, no locale, no usage) should happen before looking up the source unit's category; otherwise a source unit without a category, such as a currency, masks the real problem with a RangeError when the options themselves are what is wrong. This also matches the expected eventual structure sketched in #95, where the source unit lookup comes after option validation.

gibson042

I think this is still slightly too far off from #95.

gibson042 · 2026-08-19T14:13:42Z

+    <emu-clause id="sup-amount-selecttargetunit" type="abstract operation">
+      <h1>
+        SelectTargetUnit (
+          _sourceValue_: a Number,


This input should probably be a mathematical value. https://github.com/unicode-org/cldr/blob/main/common/supplemental/units.xml contains <unitPreference regions="001" geq="0.1">kilometer</unitPreference>, and we're just lucky that the corresponding IEEE 754 binary64 value is slightly above 0.1 rather than slightly below it (otherwise it would incorrectly not be selected for 0.1_𝔽).

Suggested change

_sourceValue_: a Number,

_sourceValue_: an extended mathematical value or *NaN*,

(and likewise throughout this PR, including in spec.emu)

gibson042 · 2026-08-19T14:42:22Z

+        1. Let _locale_ be ? Get(_options_, *"locale"*).
+        1. Let _usage_ be ? GetOption(_options_, *"usage"*, ~string~, ~empty~, *undefined*).


This will result in observably reading "locale" and "usage" after "fractionDigits", "roundingMode", "significantDigits", and "unit" (i.e., out of alphabetical order) if and only if the implementation includes ECMA-402. See #95 more a more complete writeup.

gibson042 · 2026-08-19T14:46:40Z

+        1. Let _requestedLocales_ be ? CanonicalizeLocaleList(_locale_).
+        1. If _requestedLocales_ is an empty List, let _resolvedLocale_ be DefaultLocale(); else let _resolvedLocale_ be the first element of _requestedLocales_.


This should use actual locale negotiation rather than just picking the first element; again, see #95.

gibson042 · 2026-08-19T14:51:42Z

+        1. Let _unit_ be ~unset~.
+        1. For each element _entry_ of _preferredUnits_, do
+          1. Set _unit_ to _entry_.[[Unit]].
+          1. Let _convertedValue_ be ? ConvertUnitValue(_sourceValue_, _sourceUnit_, _unit_).


It's a bit awkward to specify O(n) ConvertUnitValue calls (n - 1 in SelectTargetUnit and the last in Amount.prototype.convertTo). I'm not objecting, but we should look for ways to improve that.

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

eemeli force-pushed the convert-options branch from 46f7cdf to 3c8bebf Compare May 17, 2026 19:45

eemeli requested a review from jessealama May 17, 2026 19:50

jessealama approved these changes May 18, 2026

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jessealama force-pushed the convert-options branch 2 times, most recently from 57854cf to d3b7e95 Compare August 18, 2026 09:20

eemeli and others added 15 commits August 19, 2026 10:29

Add GetAmountConvertToUnit definitions to both ECMA-262 and ECMA-402

beaa864

Include sourceUnit & region in GetPreferredAmountUnit arguments inste…

7a0f1db

…ad of locale

We also need sourceValue for some preferences

fa6f844

Add full implementation, with data from CLDR

542c61f

Apply suggestions from code review

ee09284

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Call GetAmountOptions from GetAmountConvertToOptions to handle common…

d7ad248

… options

Add usage fallbacking

a674e82

Include editorial note with TODO for region containment fallbacking

eea2373

Update intl.emu

667a0dd

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Update intl.emu

ceffe28

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Rename GetAmountConvertToUnit to SelectTargetUnit

281f89a

Check the source unit category before reading conversion options

5e2ef52

GetAmountoptions: Broaden description (no just construction)

de966cd

Improve description of GetAmountConvertToOptions

964a6d1

jessealama force-pushed the convert-options branch from fd51602 to 964a6d1 Compare August 19, 2026 08:31

jessealama added 2 commits August 19, 2026 14:04

Read the locale option before the usage option

29fbabd

Options should be read in alphabetical order (see #95 and review feedback on #110), and alphabetically "locale" precedes "usage".

jessealama mentioned this pull request Aug 19, 2026

GetPreferredUnits asserts constraints on its region argument instead of expressing them in the parameter type #151

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jessealama requested a review from gibson042 August 19, 2026 12:14

gibson042 suggested changes Aug 19, 2026

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jessealama and others added 5 commits August 19, 2026 17:13

Update intl.emu

3404bf8

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Update intl.emu

e8bf32d

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Update intl.emu

aa4186b

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Update spec.emu

d962dc7

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

Update spec.emu

e8c2ab6

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>

	_sourceValue_: a Number,
	_sourceValue_: an extended mathematical value or NaN,

		1. Let _locale_ be ? Get(_options_, "locale").
		1. Let _usage_ be ? GetOption(_options_, "usage", ~string~, ~empty~, undefined).

		1. Let _requestedLocales_ be ? CanonicalizeLocaleList(_locale_).
		1. If _requestedLocales_ is an empty List, let _resolvedLocale_ be DefaultLocale(); else let _resolvedLocale_ be the first element of _requestedLocales_.

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eemeli commented May 16, 2026 •

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