@peculiar/asn1-schema

Decorators and helper APIs for declaring ASN.1 schemas in TypeScript.

This is the core package used by the schema modules in this repository. It lets you describe DER structures with decorators and convert them with AsnConvert, AsnParser, and AsnSerializer.

Installation

npm install @peculiar/asn1-schema

Breaking Changes In v3

v3 is ESM-only and requires Node.js ^20.19.0 || >=22.12.0 (was >=14). CommonJS code can still require("@peculiar/asn1-schema") on these versions; Node.js 22.0–22.11 can't. The public API is unchanged. See the full notes.

• TypeScript compiling to CommonJS: use "module": "node20" or "nodenext" (node16 fails with TS1479). ESM and bundler setups need no changes.
• Jest in CommonJS mode: switch to ESM mode or Vitest, or configure an ESM-to-CommonJS transformer and make sure transformIgnorePatterns doesn't exclude the @peculiar/* packages and asn1js.
• Deep imports (@peculiar/asn1-schema/build/...) are blocked by exports; import from @peculiar/asn1-schema.
• asn1js 4 is a peer dependency (v2 depended on asn1js 3). npm installs it automatically; if your app imports asn1js too, use v4. The converters check instanceof asn1js.*, so values you pass in must come from the same asn1js copy. See the asn1js 4 breaking changes for encoding differences.

Overview

Abstract Syntax Notation One (ASN.1) is widely used across X.509, PKCS, CMS, OCSP, and related standards. This package keeps those mappings declarative and type-friendly by attaching schema metadata directly to classes.

TypeScript Example

import { AsnConvert, AsnProp, AsnPropTypes, AsnType, AsnTypeTypes } from "@peculiar/asn1-schema";

@AsnType({ type: AsnTypeTypes.Sequence })
class BasicConstraints {
  @AsnProp({ type: AsnPropTypes.Boolean, defaultValue: false })
  public cA = false;
}

const basicConstraints = new BasicConstraints();
basicConstraints.cA = true;

const encoded = AsnConvert.serialize(basicConstraints);
const decoded = AsnConvert.parse(encoded, BasicConstraints);

console.log(decoded.cA);

Related Links

• Decorators overview
• ASN.1 playground