Bitfield Docs

The public JavaScript Runtime Kit API has one request function and one React read hook. Everything else stays outside app code.

Use this page when you need exact names, shapes, and failure boundaries. If you want to build a first feature, start with Package to screen. If you want copyable recipes, start with Runtime Kit Cookbook.

Public imports

import {
  sendRequestToBitfieldTarget,
  type BitfieldTargetReply,
  type BitfieldTargetRequest,
} from '@bitfield/runtime-kit';
import { useBitfieldData } from '@bitfield/runtime-kit/react';

Import path	Public value	Use it for	Not public from that path
`@bitfield/runtime-kit`	`sendRequestToBitfieldTarget(...)`	User actions that call a named target.	Read hooks, package parsing, target implementations, connection setup.
`@bitfield/runtime-kit`	`BitfieldTargetRequest`, `BitfieldTargetReply`	TypeScript request/reply annotation.	Target-specific payload/reply schemas.
`@bitfield/runtime-kit/react`	`useBitfieldData(...)`	React surfaces that read named data.	Providers, scopes, selector factories, subscriptions, address readers.

The source guard is packages/js/src/public-surface.test.ts: the root package exports only sendRequestToBitfieldTarget, and the React subpath exports only useBitfieldData.

`sendRequestToBitfieldTarget(...)`

function sendRequestToBitfieldTarget(
  request: BitfieldTargetRequest,
  signal?: AbortSignal,
): Promise<BitfieldTargetReply>;

This function sends one payload to one named target and returns reply bytes.

Request type

type BitfieldTargetRequest = {
  readonly target: string;
  readonly payload?: unknown;
};

Field	Type	Required	Constraints	Example	Common error
`target`	`string`	yes	Must be a non-empty public action name.	`"help.search"`	Empty or non-string targets fail before the request is sent.
`payload`	`unknown`	no	Converted to bytes before dispatch. Use the action reply shape to decide how to encode meaning.	`{ query: "pricing" }`	Sending a shape the target does not understand returns a target-level failure.

Payload conversion

Payload value	Bytes sent	Use when	Watch out
`Uint8Array`	Same bytes.	You already own exact bytes.	The target must know the byte format.
`string`	UTF-8 text bytes.	The target expects text.	This is not JSON unless the string itself is JSON text.
object or array	`JSON.stringify(value)` as UTF-8 bytes.	The target expects JSON.	Functions, symbols, and unsupported JSON values do not become useful data.
number or boolean	`JSON.stringify(value)` as UTF-8 bytes.	The target expects a JSON scalar.	The target still receives bytes, not a JavaScript value.
`null` or omitted	Empty bytes.	The target needs no payload.	If the target needs JSON `null`, wrap it, for example `{ value: null }`.

Reply type

type BitfieldTargetReply = {
  readonly payload: Uint8Array;
};

Field	Type	Meaning	Decode rule
`payload`	`Uint8Array`	Opaque reply bytes from the target.	Decode according to the action reply shape, not according to Runtime Kit guesses.

Cancellation

Pass an AbortSignal as the second argument when the request is tied to a UI lifetime or a changing user input.

const controller = new AbortController();

const replyPromise = sendRequestToBitfieldTarget(
  {
    target: 'help.search',
    payload: { query: 'activate device' },
  },
  controller.signal,
);

controller.abort();

Runtime Kit passes the signal to the target transport. App code should still render a recoverable state because the user action may already have left the screen.

Complete valid example

import { sendRequestToBitfieldTarget } from '@bitfield/runtime-kit';

type SearchReply = {
  results: { title: string; url: string }[];
};

export async function searchHelp(query: string): Promise<SearchReply> {
  const reply = await sendRequestToBitfieldTarget({
    target: 'help.search',
    payload: { query },
  });

  return JSON.parse(new TextDecoder().decode(reply.payload)) as SearchReply;
}

This is valid because the app calls the public action name, sends a target-owned JSON payload, and decodes the reply according to the target’s documented contract.

Invalid example

import { runSearchDirectly } from '../slots/help-search';

export async function searchHelp(query: string) {
  return runSearchDirectly({ query });
}

This is invalid because the app imports the target implementation. The public files and names is the action name plus bytes. Direct implementation imports make the app depend on how the target is built.

Error categories

Symptom	Public category	What app code should do
`sendRequestToBitfieldTarget(...) requires a non-empty target`	Bad request shape	Fix the caller. This is not a retry problem.
Runtime Kit says it is not booted or not connected	App surface is mounted without the Runtime Kit owner wiring	Show a setup/support state. Do not import setup machinery into app components.
Request fails after dispatch	Target or transport failure	Render failure state, keep the user action retryable, and log the action name plus safe payload shape.
Reply cannot be decoded	Caller and target disagree on reply shape	Fix the action reply shape or caller decoder together.

`useBitfieldData(...)`

function useBitfieldData<T>(
  selector?:
    | string
    | {
        input?: string;
        params?: Record<string, unknown>;
      },
): {
  data: T | null;
  loading: boolean;
  error: Error | null;
};

This hook reads named data for a React surface. A data name is a public name that Runtime Kit already resolved behind the surface. It is not a storage path.

Selector forms

Selector	Meaning	Example	Use when
omitted	Read the default data name for the current surface.	`useBitfieldData<WelcomeCopy>()`	The surface owns one main data input.
string	Read a named data name.	`useBitfieldData<Checklist>('launch-checklist')`	The surface has multiple named inputs.
object with `input`	Read a named data name.	`useBitfieldData({ input: 'welcome-copy' })`	You want object form for clarity or future params.
object with `input` and `params`	Read a parameterized data name.	`useBitfieldData({ input: 'help-results', params: { query } })`	Runtime Kit owns a data name that accepts local selection params.

Return state

Field	Type	Meaning	Render obligation
`data`	`T	null`	Current prepared value, or no ready value yet.	Render empty/loading state instead of assuming data exists.
`loading`	`boolean`	Runtime Kit is preparing or waiting for the value.	Show a loading state that can coexist with stale or empty UI.
`error`	`Error	null`	The read failed.	Show a recoverable error state and keep the component mounted safely.

Complete valid example

import { useBitfieldData } from '@bitfield/runtime-kit/react';

type WelcomeCopy = {
  headline: string;
  body: string;
};

export function WelcomePanel() {
  const welcome = useBitfieldData<WelcomeCopy>('welcome-copy');

  if (welcome.loading) return <p>Loading welcome copy...</p>;
  if (welcome.error) return <p>Could not load welcome copy.</p>;
  if (!welcome.data) return <p>No welcome copy yet.</p>;

  return (
    <section>
      <h2>{welcome.data.headline}</h2>
      <p>{welcome.data.body}</p>
    </section>
  );
}

This is valid because the component asks for a data name by name and renders every public state: loading, error, empty, and ready.

Invalid example

import { readPackageRecord } from '@bitfield/runtime-kit/internal/records';

export function WelcomePanel() {
  const welcome = readPackageRecord('package::launch-product::welcome-copy');
  return <h2>{welcome.headline}</h2>;
}

This is invalid because React code imports private machinery and guesses a storage address. The surface should ask for the data name.

Boundary summary

Public app code may do	Public app code must not do
Import `sendRequestToBitfieldTarget` from `@bitfield/runtime-kit`.	Import connection setup, transport, target implementation, package parser, or address helpers.
Import `useBitfieldData` from `@bitfield/runtime-kit/react`.	Import read scopes, providers, selector factories, subscription lanes, or address readers.
Send action names and payload bytes/data.	Call target implementation files directly.
Read data names.	Build storage addresses or parse package files inside components.
Decode replies according to the action reply shape.	Assume Runtime Kit understands target-specific JSON fields.

Need	Page
First end-to-end feature	Package to screen
Read-hook guide	Read data in React
Request guide	Send a request
Package fields	Package file
Complete recipes	Runtime Kit Cookbook
AI-agent guardrails	Build with AI agents

Use Runtime Kit

Understand Runtime Kit

Build without tangled code

Runtime Kit Cookbook

Reference

Runtime Kit API

Public imports

`sendRequestToBitfieldTarget(...)`

Request type

Payload conversion

Reply type

Cancellation

Complete valid example

Invalid example

Error categories

`useBitfieldData(...)`

Selector forms

Return state

Complete valid example

Invalid example

Boundary summary

​Public imports

​sendRequestToBitfieldTarget(...)

​Request type

​Payload conversion

​Reply type

​Cancellation

​Complete valid example

​Invalid example

​Error categories

​useBitfieldData(...)

​Selector forms

​Return state

​Complete valid example

​Invalid example

​Boundary summary

​Related pages

Public imports

`sendRequestToBitfieldTarget(...)`

Request type

Payload conversion

Reply type

Cancellation

Complete valid example

Invalid example

Error categories

`useBitfieldData(...)`

Selector forms

Return state

Complete valid example

Invalid example

Boundary summary

Related pages