@nrz/fast-split

This is a very fast alternative to String.split(), which can be used to quickly parse a small-to-medium sized string by a given delimiter.

It's fast · Usage

How Fast Is It!?

About 1.5x faster than str.split() for splitting short strings by a short delimiter, about 1.1-1.3x when walking or transforming the resulting list, and about 1.9x when limiting the result to 2 or 3 parts (a dedicated fast path, see src/index.ts).

Note: V8 caches split() results (no limit) for internalized strings (literals, JSON keys, short JSON values), so splitting the same such string repeatedly, as benchmarks over literals do, favors native split(). Substrings, regex captures and built strings don't hit that cache, and with many distinct internalized strings the cache is a net cost.

Linux x64, node 26.11.1. Counts are operations per ms, splitting the string '1.2.3-asdf+foo' (built at runtime) by the delimiter '.', transforms calling part.toUpperCase(), and limits at 2 items

              split 4339.624
          fastSplit 6849.283
    splitEmptyCheck 4190.307
fastSplitEmptyCheck 4803.402
 splitTransformLoop 2772.453
  splitTransformMap 2904.390
 fastSplitTransform 3465.690
         splitLimit 5491.101
     fastSplitLimit 10384.471

Usage

import { fastSplit } from '@nrz/fast-split'

// say we want to split a string on '.' characters
const str = getSomeStringSomehow()

// basic usage, just like str.split('.'), gives us an array
const parts = fastSplit(str, '.')

// get just the first two parts, leave the rest intact
// Note: unlike str.split('.', 3), the 'rest' here will
// include the entire rest of the string.
// If you do `str.split('.', 3)`, then the last item in the
// returned array is truncated at the next delimiter
const [first, second, rest] = fastSplit(str, '.', 3)

// If you need to transform it, say if it's an IPv4 address
// that you want to turn into numbers, you can do that by
// providing the onPart method, which will be slightly faster
// than getting an array and subsequently looping over it
// pass `-1` as the limit to give us all parts
const nums = fastSplit(str, '.', -1, (part, parts, index) =>
  Number(part),
)