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Fetch data on the server and client with an RPC style interface.

RPC is a natural way of expressing that a server-side function should be run in response to a client-side function call. Unlike RESTful architectures, RPC-based architectures are not required to conform to statelessness constraints and are free to return session-scoped data. Additionally, the semantics of RPC calls are not constrained by the availability of suitably-descriptive HTTP methods and RPC calls can express complex state change requests more naturally as verbs (e.g. returnProduct(id)) rather than object-orientation (e.g. PATCH /api/orders/:id).

If you're using React/Redux, you should use fusion-plugin-rpc-redux-react instead of this package.

Table of contents


yarn add fusion-plugin-rpc


import {createPlugin} from 'fusion-core';
export default createPlugin({
  deps: {RPC: RPCToken},
  middleware: ({RPCFactory}) => (ctx, next) => {
    RPC.from(ctx).request('getUser', 1).then(console.log);


// src/main.js
import React from 'react';
import App, {createPlugin} from 'fusion-core';
import RPC, {
} from 'fusion-plugin-rpc';
import UniversalEvents, {
} from 'fusion-plugin-universal-events';
import {FetchToken} from 'fusion-tokens';
import fetch from 'unfetch';

// Define your rpc methods server side
const handlers = __NODE__ && {
  getUser: async (args, ctx) => {
    return {some: 'data' + args};
  test: async (args, ctx) => {
    // Error Handling Example
    try {
    } catch (e) {
      const error = new ResponseError('Failed to do thing');
      error.code = 'DOTHING';
      error.meta = {
        custom: 'metadata',
      throw error;

export default () => {
  const app = new App(<div />);

  app.register(RPCToken, RPC);
  app.register(UniversalEventsToken, UniversalEvents);
    ? app.register(RPCHandlersToken, handlers)
    : app.register(FetchToken, fetch);

  return app;


Registration API

import RPC from 'fusion-plugin-rpc';

The RPC plugin. Provides the RPC service API.

import {RPCToken} from 'fusion-plugin-rpc-redux-react';

The canonical token for the RPC plugin. Typically, it should be registered with the RPC plugin.



Required. See https://github.com/fusionjs/fusion-plugin-universal-events#api

import {RPCHandlersToken} from 'fusion-plugin-rpc-redux-react';

Configures what RPC handlers exist. Required. Server-only.

type RPCHandlers = Object<string, () => any>

You can register a value of type RPCHandlers or a Plugin that provides a value of type RPCHandlers.


Required. Browser-only. See https://github.com/fusionjs/fusion-tokens#fetchtoken


Required. See https://github.com/fusionjs/fusion-plugin-react-redux


Required. See https://github.com/fusionjs/fusion-plugin-react-redux

Service API

const rpc: RPC = Rpc.from((ctx: Context));
  • ctx: Context - Required. A Fusion.js context

  • returns rpc: {request: (method: string, args: any) => Promise<any>}

    • request: (method: string, args: any) => Promise<any> - Makes an RPC call via an HTTP request. If on the server, this will directly call the method handler with (args, ctx).

    If on the browser, this will POST to /api/${method} endpoint with JSON serialized args as the request body. The server will then deserialize the args and call the rpc handler. The response will be serialized and send back to the browser.

    • method: string - Required. The RPC method name
    • args: any - Optional. Arguments to pass to the server-side RPC handler. Must be JSON-serializable.


The package also exports a mock RPC plugin which can be useful for testing. For example:

import {mock as MockRPC, RPCToken} from 'fusion-plugin-rpc';

app.register(RPCToken, mock);

Error Handling

Use the ResponseError error subclass for sending error responses. If this error class is not used, a generic message will be sent to the client.

import {ResponseError} from 'fusion-plugin-rpc';

function testHandler() {
  try {
  } catch (e) {
    const error = new ResponseError('Failed to do thing');
    error.code = 'DOTHING';
    error.meta = {
      custom: 'metadata',
    throw error;

Generating mock RPC handlers from fixtures

The package also exports a getMockRpcHandlers util which can be useful for testing. Fixtures need to be of the following type

type RpcResponse = Object | ResponseError;
type RpcResponseMap = Array<{
  args: Array<*>,
  response: RpcResponse,
type RpcFixtureT = {[string]: RpcResponseMap | RpcResponse};

getMockRpcHandlers has the following interface:

type getMockRpcHandlersT = (
  fixtures: Array<RpcFixtureT>,
  onMockRpc?: OnMockRpcCallbackT
) => HandlerType;

For example:

import {getMockRpcHandlers, ResponseError} from 'fusion-plugin-rpc';

const rpcFixtures = [
    getUser: {
      firstName: 'John',
      lastName: 'Doe',
      uuid: 123,
    updateUser: [{
      args: [{firstName: 'Jane'}],
      response: {
        firstName: 'John',
        lastName: 'Doe',
        uuid: 123,
    }, {
      args: [{firstName: ''}],
      response: new ResponseError('Username cant be empty'),

const mockRpcHandlers = getMockRpcHandlers(rpcFixtures);

const user = await mockRpcHandlers.getUser();

try {
  const user = await mockRpcHandlers.updateUser({firstName: ''});
} catch (updatedUserError) {
  // When error object is passed as response in fixtures,
  // it will be considered as a failure scenario and will be thrown by rpc handler.