Inline your callbacks

closure_bench.ts

const f = (g: (x: number) => number) => (x: number) => g(x)

Deno.bench("closure directly", { baseline: true }, () => {
	const foo = [...Array(1000).keys()].map(f((x) => x + 1))
})

Deno.bench("closure indirectly", () => {
	const g = f((x) => x + 1)
	const foo = [...Array(1000).keys()].map(g)
})

Deno.bench("closure very indirectly", () => {
	const g = (x: number) => x + 1
	const h = f(g)
	const foo = [...Array(1000).keys()].map(h)
})

gistfile1.txt

benchmark                    time (avg)        iter/s             (min … max)       p75       p99      p995
----------------------------------------------------------------------------- -----------------------------
closure directly              17.2 µs/iter      58,139.5  (15.62 µs … 328.54 µs)  16.08 µs  64.62 µs  68.96 µs
closure indirectly            21.5 µs/iter      46,522.4  (19.92 µs … 130.17 µs)  20.75 µs  72.04 µs  77.75 µs
closure very indirectly      21.39 µs/iter      46,744.3  (19.88 µs … 518.67 µs)  20.62 µs  31.25 µs  96.71 µs

summary
  closure directly
   1.24x faster than closure very indirectly
   1.25x faster than closure indirectly