node-asn1 is a library for encoding and decoding ASN.1 datatypes in pure JS. Currently BER encoding is supported; at some point I'll likely have to do DER.
Mostly, if you're actually needing to read and write ASN.1, you probably don't need this readme to explain what and why. If you have no idea what ASN.1 is, see this: ftp://ftp.rsa.com/pub/pkcs/ascii/layman.asc
The source is pretty much self-explanatory, and has read/write methods for the common types out there.
The following reads an ASN.1 sequence with a boolean.
var Ber = require('asn1').Ber; var reader = new Ber.Reader(Buffer.from([0x30, 0x03, 0x01, 0x01, 0xff])); reader.readSequence(); console.log('Sequence len: ' + reader.length); if (reader.peek() === Ber.Boolean) console.log(reader.readBoolean());
The following generates the same payload as above.
var Ber = require('asn1').Ber; var writer = new Ber.Writer(); writer.startSequence(); writer.writeBoolean(true); writer.endSequence(); console.log(writer.buffer);
npm install asn1