NanoTypes

Minimal, runtime-safe type guards for modern JavaScript.

Tree-shakable ESM bundle, zero-config, developer-friendly guards for typeof, instanceof, and structural checks.

• Minified: ~2.5 KB
• Gzipped: ~1.3 KB

Features

• Runtime-safe typeof and instanceof matching
• Dynamic support for global constructors (Map, URL, etc.)
• Safe in Node, browsers, and workers (no browser-global crashes)
• Non-throwing instanceof checks (runtime hardened)
• Dev-only logging via globalThis.__DEV__ or NODE_ENV !== "production"
• Auto-generated assertType.* versions
• No dependencies
• Works in any modern JS runtime (Node, browser, workers, edge)

Runtime Safety

NanoTypes is hardened for modern environments:

• Safe access of globalThis constructors
• No crashes from missing browser globals (e.g., HTMLElement in Node)
• Defensive instanceof handling
• Works consistently across Node, browsers, workers, and edge runtimes

Install

npm install nanotypes

Usage

import { is, assertType, describe } from 'nanotypes';

if (is.string("hello")) {
  console.log("It's a string!");
}

if (is(someValue, HTMLElement)) {
  someValue.focus();
}

if (is.textNode(document.createTextNode("x"))) {
  // Safe to access nodeValue, etc.
}

assertType.promise(Promise.resolve()); // throws TypeError if invalid

console.log(describe.value(new Map())); // "Map"

API

Generic Matcher

is(value, Class)

• Uses instanceof internally
• Logs warnings in development (globalThis.__DEV__ = true or when process.env.NODE_ENV !== "production")
• Never throws — safely returns false on invalid constructor input

Type-Specific Guards

Over 60 guards are exposed automatically:

| Guard | Description | | ----------------------- | ---------------------------------------- | | is.string(x) | typeof x === "string" | | is.numberSafe(x) | Safe number (non-NaN) | | is.boolean(x) | Boolean primitive | | is.defined(x) | Not null or undefined | | is.nullish(x) | null or undefined | | is.array(x) | Array literal check | | is.object(x) | Non-null object, not array | | is.objectStrict(x) | Exactly a {} object | | is.plainObject(x) | Object with prototype Object or null | | is.func(x) | Function check | | is.map(x) | Instance of Map | | is.date(x) | Instance of Date | | is.error(x) | Instance of Error | | is.textNode(x) | DOM Text node | | is.htmlElement(x) | HTMLElement node | | is.contentEditable(x) | Editable DOM node | | is.positiveNumber(x) | Greater than 0 | | is.negativeNumber(x) | Less than 0 | | is.integer(x) | Whole number | | is.finite(x) | Not Infinity, not NaN | | is.truthy(x) | Coerces to true | | is.falsy(x) | Coerces to false |

Assertive Guards

All is.* functions have an assertType.* equivalent:

assertType.url(x) // throws TypeError if not a URL

Philosophy

Make JavaScript safer without making it heavier.

NanoTypes avoids boilerplate and unnecessary runtime bloat. Just clean, modern type guards ready for anything from browser UIs to CLI tools.

0.0.8

• Hardened cross-runtime safety
• Safe global constructor detection
• Improved development-mode detection
• Optimized bundled distribution for faster Node imports

License

DR.WATT v3.0