Post #1754478

2026-04-16 15:38 UTC

JavaScript addition using the new and upcoming Math.sumPrecise(): ❌ 1 + 0.1 - 1 = 0.10000000000000009 ✅ Math.sumPrecise([1,.1,-1]) = 0.1 ❌ 1e20 + 0.1 - 1e20 = 0 ✅ Math.sumPrecise([1e20,.1,-1e20]) = 0.1 ❌ 0.1 + 0.2 = 0.30000000000000004 ❌ Math.sumPrecise([.1,.2]) = 0.30000000000000004 Read more on MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sumPrecise

Replies (6)

@AmeliaBR@front-end.social 2026-04-16 15:44

@zachleat Coming soon to a JS API near you: Math.sumPreciserFinalv2UseThisOne()

Open ##1779474
@ardouglass@mastodon.social 2026-04-16 16:01

@zachleat I love that due to backwards compatibility we can’t simply fix the plus sign. Some library out there (probably MooTools) certainly used floating point math errors in a load bearing way that would cause the web to fall apart if changed.

Open ##1779483
@ardouglass@mastodon.social 2026-04-16 16:07

@zachleat wait… “This still cannot avoid the 0.1 + 0.2 precision problem”

Open ##1779485
@chriskirknielsen@front-end.social 2026-04-16 16:17

@zachleat Dang I thought the last scenario would be solved by this. 😬 Should have been called `sumLossless`, given that it is not actually precise for that typical `.1+.2` example. Ah well, what can you do!

Open ##1779489
@loucyx@mastodon.social 2026-04-16 17:07

@zachleat OMG this is great! I guess is time to retire my library then 😂 https://coven.to/math

Open ##1779492
@mottokrosh@social.mottokrosh.com 2026-04-17 14:34

@zachleat Math.sumVibe() when?

Open ##1779498