Generate Swift / Kotlin types

A native WebView host written in Swift or Kotlin cannot import a TypeScript contract directly. webview-bridge-kit-gen reads message names and payload / response types from the contract and generates native code.

The output includes DTOs, BridgeHandlers, runtime bindings, and type-safe event functions. See Using it in Swift or Using it in Kotlin for platform wiring.

Setup

The generator uses the TypeScript compiler API. typescript is an optional peer dependency, so install it in the project that runs the generator.

npm install webview-bridge-kit
npm install --save-dev typescript

By default, the contract file must export a value named contract.

// bridge-contract.ts
import { command, defineContract, event, request } from 'webview-bridge-kit';
import { z } from 'zod';

export const contract = defineContract({
  KAKAO_LOGIN: request({
    response: z.object({
      accessToken: z.string(),
      expiresIn: z.number().optional(),
    }),
  }),
  SEND_LOGS: command({ payload: z.object({ lines: z.array(z.string()) }) }),
  OPEN_CAMERA: command(),
  PHOTO_TAKEN: event({
    payload: z.object({
      uri: z.string(),
      meta: z.object({ width: z.number(), height: z.number() }),
    }),
  }),
});

This does not inspect the schema library's runtime objects. It reads the types TypeScript inferred into the __req, __res, and __payload phantom fields, so any schema shaped like parse(value): T works.

Generate Swift

npx webview-bridge-kit-gen \
  --contract ./bridge-contract.ts \
  --lang swift \
  --out ./ios/BridgeTypes.swift

Omit --out to write to standard output. The result contains message-name enums, Codable structs, a handler protocol, and runtime binding code.

enum BridgeRequestName: String, Codable {
    case KAKAO_LOGIN
}

struct KakaoLoginResponse: Codable {
    let accessToken: String
    let expiresIn: Double?
}

Generate Kotlin

npx webview-bridge-kit-gen \
  --contract ./bridge-contract.ts \
  --lang kotlin \
  --package com.example.bridge \
  --out ./android/BridgeTypes.kt

The default --package is generated. Generated data types and handler bindings use the Android runtime's kotlinx.serialization setup.

enum class BridgeRequestName {
    KAKAO_LOGIN
}

@Serializable
data class KakaoLoginResponse(
    val accessToken: String,
    val expiresIn: Double? = null
)

Options

Option	Required	Description
--contract <file.ts>	yes	TypeScript file containing the contract
--lang <swift|kotlin>	yes	Output language
--out <file>	no	Output file; omit to use standard output
--export <name>	no	Contract export name; defaults to contract
--package <name>	no	Kotlin package; defaults to generated

Use --export if the contract has a different export name.

npx webview-bridge-kit-gen --contract ./bridge-contract.ts --export appBridge --lang swift

Type mapping and limits

TypeScript	Swift	Kotlin
string	String	String
number	Double	Double
boolean	Bool	Boolean
T[]	[T]	List<T>
object	separate Codable struct	separate @Serializable data class
optional field	T?	T? = null

JSON has only one numeric type, so TypeScript number always becomes Double. The generator stops with an error for types it cannot map safely, including unions, Date, bigint, and tuples, instead of emitting misleading code.

Nullable/optional object fields become nullable native properties. Nullable array elements and message or field identifiers that are unsafe in Swift/Kotlin fail with an explicit error.

Treat the output as generated code

Add the command to a build script or CI so the stubs are regenerated whenever the contract changes. Generated files include a do-not-edit header.