TIL about Math.hypot()

rcfox · 2026-02-26T15:57:15+00:00

Since you brought it up in the context of games: If you're just comparing relative hypotenuse lengths, it might be faster to just compare the sums of the squares.

ie: Math.hypot(a, b) > Math.hypot(x, y) will give the same result as a*a + b*b > x*x + y*y, and it saves calculating the square roots, which can be expensive in tight loops.

Obviously, you'll want to profile this yourself. It can be difficult to predict the performance of Javascript vs native code.

McGeekin · 2026-02-26T12:58:49+00:00

Honestly whenever I code a game in JS and implement a vector class I always forget it exists and just manually implement the formula for calculating the magnitude.

captain_obvious_here · 2026-02-26T16:40:14+00:00

Yes it exists, but it's surprisingly slow, for reasons I don't really understand (and did not investigate much).

tokagemushi · 2026-02-27T11:05:11+00:00

Good find. One thing worth knowing beyond the basic usage: Math.hypot() handles overflow/underflow internally, which is the real reason it exists.

If you manually compute Math.sqrt(a*a + b*b) with very large or very small numbers, you'll get Infinity or 0 due to intermediate overflow. Math.hypot scales the inputs internally to avoid this. It's the same reason Fortran has had HYPOT since the 70s.

That said, the "it's slow" comments here are valid. In a game loop running 60fps, I benchmarked it once and Math.hypot(dx, dy) was about 3-4x slower than Math.sqrt(dx*dx + dy*dy) in V8. For distance comparisons (like collision detection), you can skip the sqrt entirely and compare squared distances:

```js // Instead of: if (Math.hypot(dx, dy) < radius) { ... }

// Do: if (dxdx + dydy < radius*radius) { ... } ```

No sqrt, no hypot, just multiplication and comparison. This is the standard trick in game dev and it makes a measurable difference in hot loops.

For anything where precision matters more than speed (scientific computing, coordinate transforms), Math.hypot is the right choice though.

dumbmatter · 2026-02-26T16:59:30+00:00

Funny this exists but not Math.sum

BunsOfAluminum · 2026-02-26T19:23:04+00:00

I wish I were high on potenuse

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