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0.11.0 • Public • Published


Assertions and typeguards as primitives

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warning: pre-v1, use at your own risks


$ npm install @httpx/assert
$ yarn add @httpx/assert
$ pnpm add @httpx/assert


  • 👉  Typeguards and assertions with a consistent style.
  • 👉  Assertions with useful default error message.
  • 👉  Return weak opaque types for boolean, strings and numbers.
  • 👉  Optimized tree-shakability, starts at 56b.
  • 👉  Don't leak values in the default assertion error messages.
  • 👉  No deps. Node, browser and edge support.


👉 Official website, GitHub Readme or generated api doc


Consistent style

Typeguards starts with isXXX and have an assertion counterpart named assertXXX.

isParsableXXX and assertParsableXXX denotes a string.

Weak opaque types

For string, number and boolean the returned type is tagged with a weak opaque type. It can optionally be used to enforce that the value was checked.

For example:

import { assertUuidV7, type UuidV7 } from '@httpx/assert';
import { HttpUnprocessableEntity } from '@httpx/exception';

const persistRecord = async (uuid: UuidV7) => {
  // uuid is compatible with string.
  return await db.raw(`insert into tbl(uuid) values (${uuid})`)

const v = 'xxx'; // unknown
assertUuidV7(v, () => new HttpUnprocessableEntity());
// 👉 v is known to be `string & WeakOpaqueContainer<'UuidV4'>`
await persistRecord(v); // will work
await persistRecord('a_string'); // won't

Assertions error messages

When an assertion fail, a native TypeError is thrown by default with a message indicating the requirement and and information about the tested value. As an example:

expect(() => assertUuid('123')).toThrow(
  new TypeError('Value is expected to be an uuid, got: string(length:3)')
expect(() => assertUuid(false, undefined, { version: 1 })).toThrow(
  new TypeError('Value is expected to be an uuid v1, got: boolean(false)')
expect(() => assertUuidV1(Number.NaN)).toThrow(
  new TypeError('Value is expected to be an uuid v1, got: NaN')
expect(() => assertUuidV3(new Error())).toThrow(
  new TypeError('Value is expected to be an uuid v3, got: Error')
expect(() => assertUuidV4(new Date())).toThrow(
  new TypeError('Value is expected to be an uuid v4, got: Date')
expect(() => assertUuidV5(() => {})).toThrow(
  new TypeError('Value is expected to be an uuid v5, got: function')
expect(() => assertUuidV7(() => {})).toThrow(
  new TypeError('Value is expected to be an uuid v7, got: function')

Alternatively it's possible to provide either a message or function returning an Error. For example:

import { assertEan13, assertStringNonEmpty } from '@httpx/assert';
import { HttpBadRequest } from '@httpx/exception';

assertEan13('123', 'Not a barcode'); // 👈 Will throw a TypeError('Not a barcode')

assertStringNonEmpty(lang, () => new HttpBadRequest('Missing language'));


Type related


import { assertNever } from '@httpx/assert';

type PromiseState = 'resolved' | 'rejected' | 'running'
const state: PromiseState = 'rejected';
switch(state) {
  case 'resolved': return v;
  case 'rejected': return new Error();
    assertNever(state); // 👈 TS will complain about missing 'running' state
    // ☝️ Will throw a TypeError in js.

PS: you can use the assertNeverNoThrow with the same behaviour except that it doesn't throw and return the value instead (no runtime error).

Object related


Name Type Comment
isPlainObject<T?> PlainObject
assertPlainObject<T?> PlainObject
import { isPlainObject, assertPlainObject } from '@httpx/assert';

// Simple case: without generic value
isPlainObject({cwol: true}); // 👈 true
isPlainObject(new Promise()); // 👈 false

// With generic value (unchecked at runtime!)
type CustomType = {
  name: string;
  deep: {
    yes: boolean | null;
const value = {
  name: 'hello',
  deep: {
    yes: true,
} as unknown;

if (isPlainObject<CustomType>(value)) {
  // Notice it's a deep partial to allow autocompletion
  value?.deep?.yes; // 👈  yes will be unknown to reflect that no runtime check was done

Number related


import { assertNumberSafeInt, isNumberSafeInt } from '@httpx/assert';

isNumberSafeInt(10n); // 👉 false
isNumberSafeInt(BigInt(10)); // 👉 false
isNumberSafeInt(Number.MAX_SAFE_INTEGER); // 👉 true
assertNumberSafeInt(Number.MAX_SAFE_INTEGER + 1); // 👉 throws

Array related


Name Type Opaque type Comment
isArrayNonEmpty unknown[] ArrayNonEmpty
assertArrayNonEmpty unknown[] ArrayNonEmpty
import { isArrayNonEmpty, assertArrayNonEmpty, type ArrayNonEmpty } from '@httpx/assert';

isArrayNonEmpty([]) // 👉 false
isArrayNonEmpty([0,1]) // 👉 true
isArrayNonEmpty([null]) // 👉 true
assertArrayNonEmpty([]) // 👉 throws

String related


Name Type Opaque type Comment
isStringNonEmpty string StringNonEmpty Trims the value
assertStringNonEmpty string StringNonEmpty Trims the value
import { assertStringNonEmpty, isStringNonEmpty, type StringNonEmpty } from '@httpx/assert';

isStringNonEmpty(''); // 👉 false
isStringNonEmpty(' '); // 👉 false: trim by default
assertStringNonEmpty(''); // 👉 throws


Name Type Opaque type Comment
isParsableSafeInt string ParsableSafeInt
assertParsableSafeInt string ParsableSafeInt
import { assertStrParsableSafeInt, isStrParsableSafeInt } from '@httpx/assert';

isStrParsableSafeInt(2); // 👉 false
isStrParsableSafeInt(`${Number.MAX_SAFE_INTEGER}`); // 👉 true
assertStrParsableSafeInt(`${Number.MAX_SAFE_INTEGER}1`); // 👉 throws


Ensure a string contains a strict iso datetime with microseconds and utc suffix (aka: zulu time). Date is checked for validity.

Name Type Opaque type Comment
isParsableStrictIsoDateZ string ParsableStrictIsoDateZ
assertParsableStrictIsoDateZ string ParsableStrictIsoDateZ
import { isParsableStrictIsoDateZ, assertParsableStrictIsoDateZ, type ParsableStrictIsoDateZ } from '@httpx/assert';

isParsableStrictIsoDateZ(new Date().toISOString()); // 👉 true
isParsableStrictIsoDateZ('2023-12-29T23:37:31.653z'); // 👉 true
isParsableStrictIsoDateZ('2023-02-29T23:37:31.653'); // 👉 false, cause no 29th february in 2023

assertParsableStrictIsoDateZ('2023-02-29T23:37:31.653z'); // 👉 throws cause no 29th february



Name Type Opaque type Comment
isUuid string UuidV1 | UuidV3 | UuidV4 | UuidV5 | UuidV7
isUuidV1 string UuidV1
isUuidV3 string UuidV3
isUuidV4 string UuidV4
isUuidV5 string UuidV5
isUuidV7 string UuidV7
assertUuid string UuidV1 | UuidV3 | UuidV4 | UuidV5 | UuidV7
assertUuidV1 string UuidV5
assertUuidV3 string UuidV3
assertUuidV4 string UuidV4
assertUuidV5 string UuidV5
assertUuidV7 string UuidV7
getUuidVersion 1 | 3 | 4 | 5 | 7
import { isUuid, isUuidV1, isUuidV3, isUuidV4, isUuidV5 } from "@httpx/assert";
import { assertUuid, assertUuidV1, assertUuidV3, assertUuidV4, assertUuidV5 } from "@httpx/assert";
import { getUuidVersion } from '@httpx/assert';

// Without version
isUuid('90123e1c-7512-523e-bb28-76fab9f2f73d'); // 👉 valid uuid v1, 3, 4 or 5

// With version
isUuidV4('d9428888-122b-11e1-b85c-61cd3cbb3210'); // 👈 or isUuidV1(''), isUuidV3(''), isUuidV5('')...;

// Utils
getUuidVersion('90123e1c-7512-523e-bb28-76fab9f2f73d'); // 5



Supported barcodes is currently limited to Ean13

import { isEan13 } from "@httpx/assert";
import { assertEan13 } from "@httpx/assert";

isEan13('1234567890128'); // 👈 will check digit too



Check whether the value is a valid tcp/udp network port (0-65535)

import { isNetworkPort } from "@httpx/assert";
import { assertNetworkPort } from "@httpx/assert";
import { type NetworkPort } from "@httpx/assert";

isNetworkPort(443); // 👈 weak opaque type is NetworkPort



Check whether the value is a specific http method (case-insensitive).

import { isHttpMethod } from "@httpx/assert";
import { assertHttpMethod } from "@httpx/assert";
import { type HttpMethod } from "@httpx/assert";

const value: unknown = 'GET';

isHttpMethod('GET', value); // 👈 weak opaque type is HttpMethod
assertHttpMethod('GET', value);


Check whether the value is a valid http method (case-insensitive).

import { isHttpValidMethod } from "@httpx/assert";
import { assertHttpValidMethod } from "@httpx/assert";
import { type HttpMethod } from "@httpx/assert";

const value: unknown = 'GET';

isHttpValidMethod(value); // 👈 weak opaque type is HttpMethod

Bundle size

Code and bundler have been tuned to target a minimal compressed footprint for the browser.

ESM individual imports are tracked by a size-limit configuration.

Scenario Size (compressed)
Import isPlainObject ~ 100b
Import isUuid ~ 175b
Import isEan13 ~ 117b
All typeguards, assertions and helpers ~ 1700b

For CJS usage (not recommended) track the size on bundlephobia.


Level CI Description
Node CI for 18.x, 20.x & 22.x.
Browsers > 95% on 12/2023. Mins to Chrome 96+, Firefox 90+, Edge 19+, iOS 12+, Safari 12+, Opera 77+
Edge Ensured on CI with @vercel/edge-runtime.
Typescript TS 5.0+ / are-the-type-wrong checks on CI.
ES2022 Dist files checked with es-check

For older browsers: most frontend frameworks can transpile the library (ie: nextjs...)


Special thanks for inspiration:


Contributions are warmly appreciated. Have a look to the CONTRIBUTING document.


If my OSS work brightens your day, let's take it to new heights together! Sponsor, coffee, or star – any gesture of support fuels my passion to improve. Thanks for being awesome! 🙏❤️

Special thanks to

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JetBrains Embie.be


MIT © belgattitude and contributors.

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