Installation

Run one of the following commands to add asn1js to your project:

npm

npm install asn1js

Yarn

yarn add asn1js

pnpm

pnpm add asn1js

Bun

bun add asn1js

Requirements

asn1js is an ES module and runs in modern browsers and in Node.js ^20.19.0 || >=22.12.0. On these Node.js versions, CommonJS code can still load it with require("asn1js").

If you compile TypeScript to CommonJS, set "module" to "node20" or "nodenext" in tsconfig.json.

First steps

Import the library and decode some bytes:

import * as asn1js from "asn1js";

const sequence = new asn1js.Sequence({
  value: [new asn1js.Integer({ value: 42 }), new asn1js.Utf8String({ value: "hello" })],
});
const der = sequence.toBER();

const { offset, result } = asn1js.fromBER(der);
if (offset === -1) {
  throw new Error(result.error);
}
console.log(result.toString());
// SEQUENCE :
//   INTEGER : 42
//   UTF8String : 'hello'

Next, browse the API reference.

Upgrading from v3

v4 is ESM-only, raises the minimum Node.js version, and changes some encoding and validation behavior. Read the breaking changes before upgrading. Upgrade libraries that depend on asn1js, such as pkijs and @peculiar/asn1-schema, at the same time, because objects from two asn1js versions fail each other's instanceof checks.