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

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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"]]

 

🚀 Install

pnpm add @nyaomaru/divider
# or npm i / yarn add

import { divider } from '@nyaomaru/divider';

 

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}`;
};

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}`;
};

👉 Easy to review at a glance.

 

Use Case 2: Mixed Delimiters in Logs

Logs often contain spaces, commas, and tabs together: 

const log = 'ERRORt2025-09-11, UserID:1234';

// regex split
log.split(/[s,]+/);
// ["ERROR", "2025-09-11", "UserID:1234"]

Readable? Not really.

With divider: 

import { divider } from '@nyaomaru/divider';

divider(log, ' ', ',', 't');
// ["ERROR", "2025-09-11", "UserID:1234"]

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"]]

With divider: 

import { divider } from '@nyaomaru/divider';

const parsed2 = divider(records, 3, 7);
// [["TOK","1234","0"], ["OSA","9876","1"]]

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"]

With divider: 

import { dividerNumberString } from '@nyaomaru/divider';

dividerNumberString(str);
// ["abc","123","def","456"]

 

📝 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"]]

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']

Path

import { pathDivider } from '@nyaomaru/divider';

pathDivider('/usr/local/bin');
// ['usr', 'local', 'bin']

pathDivider('foo|bar/baz');
// ['foo', 'bar', 'baz']

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']

 

✨ 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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