strabo

Adds array support to String.prototype.startsWith, endsWith, and includes.

"hello world".startsWith(["hi", "hello", "hey"]) // true — matches if ANY element matches
"hello world".endsWith(["world", "planet"])      // true
"hello world".includes(["xyz", "wor"])           // true

Normally these methods only accept a single string. strabo patches them so they also accept an array of strings, returning true if the string matches any element of the array — while remaining fully backward compatible with the original single-string behavior. The whole package is 4.5kb gzipped.

⚠️ This package works by mutating global prototypes. Importing it changes the behavior of String.prototype.startsWith, endsWith, and includes for your entire JavaScript environment — not just your own module. Read How it works before installing.

---

Install

npm install strabo

yarn add strabo

pnpm add strabo

Usage

As an npm package

Import it once — anywhere near your application's entry point is enough. It has no exports; importing it for its side effect is the entire API.

// ES6
import "strabo"

"John walks in the park".startsWith(["Jack", "John", "Jim"]) // true

// CommonJS
require("strabo")

"John walks in the park".startsWith(["Jack", "John", "Jim"]) // true

TypeScript users get full type support out of the box — no extra @types package needed. startsWith, endsWith, and includes are typed to accept string | string[], with autocomplete and type-checking working exactly as you'd expect for the native methods.

import "strabo"

"John walks in the park".startsWith(["Jack", "John", "Jim"]) // ✅ type-checks
"John walks in the park".startsWith(42)                      // ❌ type error, same as before

Via <script> tag (no build tool required)

A browser-ready build is available on both major CDNs:

<script src="https://unpkg.com/strabo"></script>
<script>
  console.log("hello world".startsWith(["hi", "hello"])) // true
</script>

<script src="https://cdn.jsdelivr.net/npm/strabo"></script>

Pin a version in production. An unversioned CDN URL always resolves to the latest release, which can silently change behavior under you after a future update:

<script src="https://unpkg.com/strabo@1.0.0"></script>

API

String.prototype.startsWith(searchString | searchStrings, position?)

Returns true if the string starts with the given string, or with any string in the given array.

"unit-test.spec.ts".startsWith(["unit-", "integration-"]) // true

String.prototype.endsWith(searchString | searchStrings, endPosition?)

Returns true if the string ends with the given string, or with any string in the given array.

"report.pdf".endsWith([".pdf", ".docx", ".xlsx"]) // true

String.prototype.includes(searchString | searchStrings, position?)

Returns true if the string contains the given string, or any string in the given array.

"the quick brown fox".includes(["cat", "fox", "dog"]) // true

All three retain their original single-string signature and behavior unchanged — passing a plain string behaves exactly as it always has, with the same optional position argument.

How it works

On import, strabo checks each of startsWith, endsWith, and includes to see whether the current environment already handles array input natively (in case a future JS engine implements this itself). If so, strabo does nothing for that method — it never re-wraps a method that already does the job. Otherwise, it wraps the native method: array input is handled by checking each element in turn; any non-array input is passed straight through to the original, untouched implementation.

The original native implementations are preserved and remain reachable at String.prototype.origStartsWith, origEndsWith, and origIncludes, in case you ever need to bypass the patch and call the strict, string-only original directly.

Because the patch only adds array-handling on top of existing behavior, and never changes how a plain string argument is handled, this is designed to be a safe, non-breaking addition to any codebase — including ones that use third-party libraries that also call startsWith/endsWith/includes internally with plain strings.

strabo patches each method at most once per environment, even if imported multiple times or by multiple packages in your dependency tree — repeated imports are safe and inexpensive.

Why would I want this?

Array-matching against startsWith/endsWith/includes is a common enough pattern that it usually gets hand-rolled with .some() every time it's needed:

// without strabo
const prefixes = ["Jack", "John", "Jim"]
const matches = prefixes.some(p => str.startsWith(p))

// with strabo
const matches = str.startsWith(prefixes)

strabo just lets you write the check directly, using the method you already know.

TypeScript support

Type declarations are bundled with the package — nothing extra to install. The overloaded signatures are ambient (global), so they apply automatically the moment you import "strabo" anywhere in your project; no per-file setup needed.

Browser & runtime support

strabo has no dependencies and uses only standard Object.defineProperty/Object.defineProperties APIs, so it works anywhere String.prototype.startsWith/endsWith/includes already exist — which is effectively every modern browser and Node.js version in common use today.

Contributing

Issues and pull requests are welcome. To build locally:

git clone https://github.com/emil-babayan/strabo.git
cd strabo
npm install
npm run build

License

MIT © Emil Babayan