<!-- Summary provided to audience: --> <style> /* make code examples suck less */ pre code { margin: 0 !important; font-size: 1.25em !important; } pre { padding: 0 !important; text-align: left !important; } .align-left { text-align: left !important; } .small-li li { font-size: 0.85em !important; } </style> <!-- .slide: data-cover --> # Amount: Stage 1 Update Ben Allen & Jesse Alama (Igalia, in collaboration with Google) November 2025 --- ## What is an Amount? * An Amount is a mathematical value tagged (optionally) with a unit and precision. * Its API is intentionally very small. There's no arithmetic. You can (re)tag an Amount with a different unit, and update the precision. --- ## Since last time * Amount is a frequent topic of discussion in the biweekly TC39 JS Numerics call (if you like numbers, please join us!). * In the pre-plenary JS Numerics breakout session on Monday we spent time talking about how Amount is both an Intl thing as well as *not* an Intl thing. It's a kind of numeric thing but doesn't have arithmetic. What's up with that? --- ## Returning to our roots * One year ago (2024 TC39 Japan plenary), ~~Amount~~ Measure got to stage 1. At the time, Amount definitely supported some unit conversion. * We pared the proposal down, renamed it, and focused on the handling of digit strings and precision, and largely neglected units. * We're building on [keep-trailing-zeros](https://github.com/tc39/proposal-intl-keep-trailing-zeros) regarding precision --- ## Returning to our roots * There's momentum around the [`<amount>` HTML proposal](https://github.com/mozilla/explainers/blob/main/amount.md) (including last week at W3C TPAC), in which unit conversion is a crucial part. * Instead of handwaving the story about unit conversion, maybe Amount v1 should do already *some* conversion? --- ## Which units? * We would like to convert an Amount (with unit) to another Amount, given a new unit. * Which units might make sense? Naturally, we do not want to depend on unstable data. * An initial focus could be on SI units (`meter`, `gram`, etc.) * We could conceivably add more units, such as those relevant for CSS (`em`) * See also [`CSSUnitValue`](https://developer.mozilla.org/en-US/docs/Web/API/CSSUnitValue) --- ## Which units? * Other standaridized conversions (e.g. meters to feet) could be included, following [CLDR](https://github.com/unicode-org/cldr/blob/main/common/supplemental/units.xml), which follows NIST (USA), which in turn follows the International Bureau of Weights and Measures. --- ## Proposed data model * Mathematical values (probably subject to [limits](https://docs.google.com/presentation/d/1NsezmIvFSr4qH4EXnh-cqOjikiUx196feKNM797m6fw/)), together with: NaN, ±♾️, -0 * Temporal-style static constructor `.from` that takes Numbers, BigInts, and (decimal digit) Strings * `.toString`/`.toLocaleString` for rendering * `.with` to functionally update an Amount with a new unit/precision * `.convertTo(unit: string)`: convert an Amount to another Amount with the new unit * We'd implement the [Intl unit protocol](https://github.com/sffc/proposal-intl-unit-protocol) --- ## For the committee - We believe that this sketch of Amount is in scope for 262; this is not just about presenting numbers in different locales. - Is this a worthwhile direction we want us to go in? - Would you be more on board with this vision of Amount than before? --- ## Discussion