cantonjs-codegen

Generate TypeScript types from Daml DAR files for use with cantonjs.

Install

npm install --save-dev cantonjs-codegen

Usage

cantonjs-codegen --dar ./model.dar --output ./src/generated

This reads your DAR file, extracts Daml-LF package definitions, and generates TypeScript modules.

Generated Output

Records

data Asset = Asset with
  owner : Party
  value : Int

export type Asset = {
  readonly owner: string
  readonly value: string  // Int64 -> string for precision
}

Variants

data Result = Success with value : Int
            | Failure with reason : Text

export type Result =
  | { readonly tag: 'Success'; readonly value: { readonly value: string } }
  | { readonly tag: 'Failure'; readonly value: { readonly reason: string } }

Enums

data Color = Red | Green | Blue

export type Color = 'Red' | 'Green' | 'Blue'

Templates

Templates generate companion const objects with templateId and choice definitions:

export const Asset = {
  templateId: '#my-pkg:Main:Asset' as const,
  choices: {
    Transfer: { name: 'Transfer' as const },
  },
} as const

Type Mapping

| Daml Type | TypeScript Type | Notes | |-----------|-----------------|-------| | Int / Int64 | string | Precision preservation | | Numeric n | string | Arbitrary precision | | Text | string | | | Bool | boolean | | | Party | string | | | ContractId a | string | | | Date / Time | string | ISO 8601 | | Optional a | T \| null | | | List a | readonly T[] | | | Map k v | ReadonlyMap<K, V> | |

Using Generated Types with cantonjs

import { createLedgerClient, jsonApi } from 'cantonjs'
import { Asset } from './generated/Main.js'

const client = createLedgerClient({
  transport: jsonApi({ url: 'http://localhost:7575', token: jwt }),
  actAs: 'Alice::1234',
})

// Type-safe template ID and arguments
const created = await client.createContract(Asset.templateId, {
  owner: 'Alice',
  value: '100',
})

await client.exerciseChoice(
  Asset.templateId,
  created.contractId,
  Asset.choices.Transfer.name,
  { newOwner: 'Bob' },
)

How It Works

1. Parse — extract .dalf files from the DAR (ZIP) archive using JSZip
2. Decode — parse Daml-LF protobuf with intern table resolution using protobufjs
3. Emit — generate TypeScript modules from decoded type definitions

Requirements

• Node.js >= 18

Related

• cantonjs — Core TypeScript library for Canton
• cantonjs-react — participant-private React hooks for Canton ledger apps

License

Apache-2.0