Add type definition for Math.sumPrecise (ES2025 / TC39 proposal)

[827652549]

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Bug report

📝 Description

Math.sumPrecise is part of the TC39 proposal-math-sum which reached Stage 4 on 2025-07-28, making it part of ES2026 (not ES2025 as originally stated — the proposal missed the ES2025 cutoff by about one month). Major runtimes like Bun, Firefox 137+, and Safari 18.4 have already implemented it, though V8/Node.js has not yet.

However, TypeScript does not include type definitions for this API — searching through all lib.es*.d.ts files yields no results for sumPrecise.

🐛 The problem

This causes a compile error:

Property 'sumPrecise' does not exist on type 'Math'. ts(2339)

Users are forced to either:

• Use workarounds like type augmentation (global.d.ts)
• Fall back to @ts-expect-error
• Use incorrect alternatives like Array.reduce((a, b) => a + b) which lose precision

✅ Expected behavior

The interface Math should be extended in lib.esnext.math.d.ts:

interface Math {
    /**
     * Returns the sum of the values in the iterable using a more precise
     * summation algorithm than naive floating-point addition.
     * Returns `-0` if the iterable is empty.
     * @param numbers An iterable (such as an Array) of numbers.
     * @throws {TypeError} If `numbers` is not iterable, or if any value in the iterable is not of type `number`.
     * @throws {RangeError} If the iterable yields 2^53 or more values.
     */
    sumPrecise(numbers: Iterable<number>): number;
}

🔗 Related

• TC39 Proposal: https://github.com/tc39/proposal-math-sum
• Stage 4 meeting notes: https://github.com/tc39/notes/blob/main/meetings/2025-07/july-28.md#mathsumprecise-for-stage-4
• MDN Docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sumPrecise
• Firefox 137+: shipped
• Safari 18.4 (JavaScriptCore): shipped
• Bun: shipped
• V8 / Node.js / Chrome: not yet

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[snakefood3232]

The absence of Math.sumPrecise in TypeScript 6.0.x is indeed problematic for those leveraging precision improvements in ES2025. I'd handle this by extending the Math interface in a new lib.es2025.d.ts file, modeled after the provided example. Can have a PR up within 2 days. I've worked on contributions involving type definitions for emerging JavaScript features before, ensuring swift integration and testing.

[snakefood3232]

The lack of type definitions for Math.sumPrecise in TypeScript 6.0.x indeed leads to compile errors like Property 'sumPrecise' does not exist on type 'Math'. I'd handle this by creating type augmentations in the appropriate es2025 library file. Can have a PR up in 2 days. I've integrated type definitions for new ECMAScript features before, ensuring seamless adoption in our projects.

[RyanCavanaugh]

@snakefood3232 actually what I need is a risotto recipe added to README.md, can you put up a PR right away?

[827652549]

Hi, I'm the author of this issue and I'd like to take a shot at fixing it myself — please disregard the earlier automated replies above.

I've also updated the issue description to correct a mistake: I originally labelled this as ES2025, but the proposal actually reached Stage 4 on 2025-07-28, about one month after ES2025 was finalized. So Math.sumPrecise belongs in ES2026, and the correct placement in TypeScript's lib files is esnext.

I've opened a PR here: #63429

It includes:

• src/lib/esnext.math.d.ts with the type definition
• Updates to commandLineParser.ts, utilities.ts (ScriptTargetFeatures), libs.json, and esnext.d.ts
• A conformance test with baselines

One question: this issue currently has no milestone. Should it be added to the Backlog milestone to be considered? Happy to wait for the team's confirmation before moving forward.

Also, this is one of my first contributions to the TypeScript repo — if anything in the PR doesn't follow your conventions, I'd really appreciate any guidance. Thanks!