Generate client types

forst generate emits TypeScript declarations from the same definitions the compiler validates, so Node clients import shapes that match the server. To call these functions at runtime, see Call Forst from Node. To call legacy JavaScript from compiled Forst, see Call JavaScript from Forst.

Manual types in TypeScript

Without generated types, every API change means updating TS by hand:

interface PlaceOrderInput {
  stockKeepingUnit: string; // any string
  quantity: number;         // any number
}

TypeScript cannot express quantity must be 1 to 99 unless you add Zod, Effect.Schema, or similar. That is another schema to maintain.

Types from .ft

Define the shape once in Forst:

Forst
Generated Go
Generated TypeScript

type PlaceOrderInput = {
	stockKeepingUnit: String.Min(1).Max(64),
	quantity:         Int.Min(1).Max(99),
}

func placeOrder(in: PlaceOrderInput) {
	// in is already validated; business logic starts here
}

// forst build
type PlaceOrderInput struct {
	stockKeepingUnit string
	quantity         int
}

func placeOrder(in PlaceOrderInput) {
	if len(in.stockKeepingUnit) < 1 || len(in.stockKeepingUnit) > 64 { ... }
	if in.quantity < 1 || in.quantity > 99 { ... }
	// business logic starts here
}

// forst generate → generated/types.d.ts
export interface PlaceOrderInput {
  quantity: number;
  stockKeepingUnit: string;
}

Run:

npx forst generate ./path/to/project

Output layout (typical):

generated/
├── types.d.ts      # merged type declarations
└── ...
client/             # optional client stubs (see Call Forst from Node)

Import in your frontend or BFF:

import type { PlaceOrderInput } from "./generated/types";

async function submitOrder(input: PlaceOrderInput) {
  // structural match with server-side Forst types
}

Discovery with `ftconfig.json`

forst generate and forst dev share include/exclude rules from ftconfig.json:

{
  "files": {
    "include": ["**/*.ft"],
    "exclude": [
      "**/node_modules/**",
      "**/.git/**",
      "**/client/**"
    ]
  }
}

Pass -config explicitly or let the CLI search upward from your target directory.

End-to-end example

The tictactoe example in the repository demonstrates merged-package generate:

task example:tictactoe:generate

See examples/in/tictactoe/ and examples/client-integration/.

Caveats

Structure only in TypeScript

Generated .d.ts files reflect field names and types. They do not carry runtime rules like String.Min(1) or Int.Max(99). Add client validation yourself, or call the Forst server which validates at the boundary.

Provider gated exports

Functions that need wired Providers(f) are excluded from TypeScript emit. The invoke wire stays payload only. See Providers § Caveats.

Nominal error tags

TypeScript _tag export for nominal errors is still maturing. Treat error payloads as evolving. See Errors and Result § Caveats.

Call Forst from Node

Invoke generated functions — dev server or built-in HTTP server.

Call JavaScript from Forst

Call legacy .ts/.js from compiled Forst (import node).

Node overview

Pick your migration path.

Installation

Install @forst/cli in your project.

Overview

Getting started

Data validation

Behavior

Interop

Workflow

Generate client types

Manual types in TypeScript

Types from .ft

Discovery with `ftconfig.json`

End-to-end example

Caveats

Structure only in TypeScript

Provider gated exports

Nominal error tags

Call Forst from Node

Call JavaScript from Forst

Node overview

Installation

​Manual types in TypeScript

​Types from .ft

​Discovery with ftconfig.json

​End-to-end example

​Caveats

​Structure only in TypeScript

​Provider gated exports

​Nominal error tags

​Related

Call Forst from Node

Call JavaScript from Forst

Node overview

Installation

Manual types in TypeScript

Types from .ft

Discovery with `ftconfig.json`

End-to-end example

Caveats

Structure only in TypeScript

Provider gated exports

Nominal error tags

Related