Support additional scientific notation styles?

[sffc]

Based on #164, we are adding scientific notation via { notation: "scientific" }. We are using the LDML format for the output, which is

1.23E4

Based on a localizable pattern and exponent separator:

• https://github.com/unicode-org/cldr/blob/release-35-1/common/main/en.xml#L4362
• https://github.com/unicode-org/cldr/blob/release-35-1/common/main/en.xml#L4290

However, this is not necessarily the most "human-friendly" scientific format. Users might expect something like the following:

1.23×10⁴

Users may also prefer to use HTML tags for the superscript. This also helps support non-Latin numbering systems since the superscript digits are only available in Latin.

1.23×10<sup>4</sup>

This could be specified by a new field like scientificDisplay, similar to compactDisplay.

{ notation: "scientific", scientificDisplay: "e" }  // default
{ notation: "scientific", scientificDisplay: "superscriptDigits" }
{ notation: "scientific", scientificDisplay: "html" }

[ray007]

And if you have units, SI-prefixes may be the way to go.

[markusicu]

ICU has this functionality in http://icu-project.org/apiref/icu4c/classicu_1_1ScientificNumberFormatter.html
It does not require extra CLDR data.

[Yaffle]

Btw, what MathML to use for a number in scientific notation, like 1.23×10⁻⁴ ?
<mn>1.23×10⁻⁴</mn>
or
<mrow><mn>1.23</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup></mrow>
?

[ryzokuken]

If we directly expose createMarkupInstance(), users could easily do something like the MathML example by themselves, but I'm not sure if it's too high level for an API like ecma402. Perhaps just an additional scientificDisplay: "mathml" should work better?

[sffc]

Another point: you can use formatToParts to get this behavior. Although the spec doesn't guarantee that the exponent always follows a certain pattern following the mantissa, in practice, this is true in every locale.

const nf = new Intl.NumberFormat("es-MX", { notation: "scientific" });
nf.formatToParts(5.55e-4);

/*
[
  {"type":"integer","value":"5"},
  {"type":"decimal","value":"."},
  {"type":"fraction","value":"55"},
  {"type":"exponentSeparator","value":"E"},
  {"type":"exponentMinusSign","value":"-"},
  {"type":"exponentInteger","value":"4"}
]
*/

You can search for "exponentSeparator" and replace it with "×10", and then wrap the "exponentMinusSign" and "exponentInteger" in <sup>.

[ryzokuken]

@sffc

Another point: you can use formatToParts to get this behavior.

This, on the other hand, seems too low level to me. I suppose atleast html (not quite sure about mathml yet, but I suppose that too) is a common enough use-case to be easier to achieve?

[sffc]

This, on the other hand, seems too low level to me. I suppose atleast html (not quite sure about mathml yet, but I suppose that too) is a common enough use-case to be easier to achieve?

I demonstrated that it's possible today for someone to write a small library on top of the existing Intl.NumberFormat that mostly works. That violates point 3 in API surface guidelines I proposed in #442 (comment). That being said, this feature could still move forward, but we should have a compelling case that there are a lot of users who would benefit from this feature, and that it is sufficiently difficult to implement in user land that it belongs in the standard library.

[ryzokuken]

I hadn't realized that this wasn't a WIP. I don't feel strongly enough about it unless we go ahead and add the others, thanks for the clarification.

[anba]

formatToParts was added for exactly this purpose, i.e. allowing additional html formatting.

[Yaffle]

Another variant is to extract the exponent from the number and format the coefficient and the exponent separately. Well... The accuracy will be lost for some numbers.