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Introducing `divider`: A Handy Utility to Split Strings and Arrays ✂️

#typescript #javascript #opensource #util

Hey folks!

Lately I spend more time arguing with AI than with humans… and honestly, AI wins most of the time 🤖😂
Anyway, I’m @nyaomaru, a frontend engineer!

We all split strings daily, right?

Most of the time, split() is enough. But what about those cases where things get tricky?

  • Multiple delimiters in the same string
  • Cutting by fixed positions
  • Directly handling string[] without extra loops

That’s when split + map + regex + substring turns into a mess.

So I built @nyaomaru/divider: a lightweight utility that lets you divide by delimiters or indexes, and it works on arrays too.

 

TL;DR

  • split is fine for simple cases, but becomes verbose with multiple delimiters, fixed chunks, or arrays.
  • divider gives you one-liners: divider(input, ...separatorsOrIndexes, options?).
  • Comes with helpers (dividerFirst, dividerLast, dividerLoop) and presets (emailDivider, csvDivider, pathDivider).

Example:

divider('a b,c', ' ', ','); // ['a', 'b', 'c'] divider(['TOK12340', 'OSA98761'], 3, 7); // [["TOK","1234","0"], ["OSA","9876","1"]]
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🚀 Install 

pnpm add @nyaomaru/divider # or npm i / yarn add
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import { divider } from '@nyaomaru/divider';
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Use Case 1: Fixed-length Substrings Without Boilerplate

Say you want to format ISBN codes.
Normally you’d end up chaining substring() calls:

const toISBN = (code: string): string => { if (code.length !== 10 && code.length !== 13) return ''; if (code.length === 10) { const countryCode = code.substring(0, 1); const publisherCode = code.substring(1, 3); const bookCode = code.substring(3, 9); const checkDigit = code.substring(9); return `ISBN${countryCode}-${publisherCode}-${bookCode}-${checkDigit}`; } const isbnPrefix = code.substring(0, 3); const countryCode = code.substring(3, 4); const publisherCode = code.substring(4, 6); const bookCode = code.substring(6, 12); const checkDigit = code.substring(12); return `ISBN${isbnPrefix}-${countryCode}-${publisherCode}-${bookCode}-${checkDigit}`; };
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With divider, the intent is much clearer:

import { divider } from '@nyaomaru/divider'; const toISBN = (code: string): string => { if (code.length === 10) { const [countryCode, publisherCode, bookCode, checkDigit] = divider( code, 1, 3, 9 ); return `ISBN${countryCode}-${publisherCode}-${bookCode}-${checkDigit}`; } const [isbnPrefix, countryCode, publisherCode, bookCode, checkDigit] = divider(code, 3, 4, 6, 12); return `ISBN${isbnPrefix}-${countryCode}-${publisherCode}-${bookCode}-${checkDigit}`; };
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👉 Easy to review at a glance.

 

Use Case 2: Mixed Delimiters in Logs

Logs often contain spaces, commas, and tabs together:

const log = 'ERROR\t2025-09-11, UserID:1234'; // regex split log.split(/[\s,]+/); // ["ERROR", "2025-09-11", "UserID:1234"]
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Readable? Not really.

With divider:

import { divider } from '@nyaomaru/divider'; divider(log, ' ', ',', '\t'); // ["ERROR", "2025-09-11", "UserID:1234"]
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Much simpler.

 

Use Case 3: Fixed-length Records in Arrays

Financial/banking systems often rely on fixed-length codes:

const records = ['TOK12340', 'OSA98761']; const parsed1 = records.map((r) => [ r.substring(0, 3), r.substring(3, 7), r.substring(7), ]); // [["TOK","1234","0"], ["OSA","9876","1"]]
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With divider:

import { divider } from '@nyaomaru/divider'; const parsed2 = divider(records, 3, 7); // [["TOK","1234","0"], ["OSA","9876","1"]]
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One-liner, done.

 

Use Case 4: Splitting Numbers and Letters

Parsing alphanumeric strings:

const str = 'abc123def456'; // regex gets messy str.split(/(\d+)/).filter(Boolean); // ["abc","123","def","456"]
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With divider:

import { dividerNumberString } from '@nyaomaru/divider'; dividerNumberString(str); // ["abc","123","def","456"]
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📝 Summary

If split is a cutter, divider is a multi-tool.

Especially for slightly complex string manipulations, it helps you keep code clean, readable, and maintainable.

It also works directly on string[], supports presets, and stays lightweight.

 

📋 Copy-paste Recipes

CSV 

import { divider, csvDivider } from '@nyaomaru/divider'; const lines = ['Alice,24,Engineer,Tokyo', 'Bob,30,Designer,Osaka']; divider(lines, ','); // [["Alice","24","Engineer","Tokyo"], ["Bob","30","Designer","Osaka"]] csvDivider(lines); // [["Alice","24","Engineer","Tokyo"], ["Bob","30","Designer","Osaka"]]
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Email 

import { emailDivider } from '@nyaomaru/divider'; const [local, domain] = emailDivider('nyao@example.com'); // ["nyao", "example.com"] emailDivider('nyao@example.com', { splitTLD: true }); // ['nyao', 'example', 'com']
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Path 

import { pathDivider } from '@nyaomaru/divider'; pathDivider('/usr/local/bin'); // ['usr', 'local', 'bin'] pathDivider('foo|bar/baz'); // ['foo', 'bar', 'baz']
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Other utilities 

import { dividerLast, dividerLoop } from '@nyaomaru/divider'; dividerLast('hello world', ' '); // 'world' dividerLoop('abcdefghij', 3); // ['abc', 'def', 'ghi', 'j'] dividerLoop(['hello', 'world'], 2, { flatten: true }); // ['he', 'll', 'ow', 'or', 'ld']
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✨ Links & Contribute

PRs and Issues welcome — in English or Japanese or Dutch 😺

 

Next Up

Next, I’ll switch gears a bit.
Instead of another utility, I want to talk about technical debt — that pile of “we’ll fix it later” decisions that always comes back to bite us.

The article will cover:

  • What “technical debt” actually means in real-world projects
  • Why those little “temporary hacks” keep compounding interest
  • How teams can repay debt incrementally (without betting on a risky full rewrite)

It’ll be a practical, down-to-earth deep dive, written from everyday development experience rather than just theory.

Stay tuned — I hope it helps your team reduce those “just for now” moments! 🧹

 

✂️ That’s the gist!

divider is small but handy — especially when split() alone starts to feel clunky.
I’d love to hear how you use it in your projects, or what edge cases you run into.

Drop a comment with your thoughts, or open an Issue/PR on GitHub if you’ve got ideas.
Feedback is always welcome! 🙌

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