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nice-grpc-web npm version

A Browser gRPC client library that is nice to you.


  • Written in TypeScript for TypeScript.
  • Modern API that uses Promises and Async Iterables for streaming.
  • Easy cancellation propagation with AbortSignal.
  • Middleware support via concise API that uses Async Generators.


npm install nice-grpc-web


Compiling Protobuf files

The recommended way is to use ts-proto.

Using ts-proto

Install necessary tools:

npm install protobufjs long
npm install --save-dev grpc-tools ts-proto

Use ts-proto version not older than 1.112.0.

Given a Protobuf file ./proto/example.proto, generate TypeScript code into directory ./compiled_proto:

./node_modules/.bin/grpc_tools_node_protoc \
  --plugin=protoc-gen-ts_proto=./node_modules/.bin/protoc-gen-ts_proto \
  --ts_proto_out=./compiled_proto \
  --ts_proto_opt=env=browser,outputServices=nice-grpc,outputServices=generic-definitions,outputJsonMethods=false,useExactTypes=false \
  --proto_path=./proto \

You can omit the --plugin flag if you invoke this command via npm script.

When running on Windows command line, you may need to wrap the ts_proto_opt value with double quotes:

Using google-protobuf

Install necessary tools:

npm install google-protobuf
npm install --save-dev grpc-tools ts-protoc-gen @types/google-protobuf

Given a Protobuf file ./proto/example.proto, generate JS code and TypeScript definitions into directory ./compiled_proto:

./node_modules/.bin/grpc_tools_node_protoc \
  --plugin=protoc-gen-ts=./node_modules/.bin/protoc-gen-ts \
  --js_out=import_style=commonjs,binary:./compiled_proto \
  --ts_out=service=grpc-web:./compiled_proto \
  --proto_path=./proto \

Preparing the server

Browsers can't talk directly to a gRPC server and require a specialized proxy.

It is recommended to use Envoy proxy with grpc_web filter. For an example of how to configure Envoy, see the config that we use in our tests.

In Kubernetes, use Contour ingress controller, which is based on Envoy and has grpc_web filter enabled by default.

Another option is to use traefik with GrpcWeb middleware (available in traefik 3.0.0-beta1).

Another option is to use improbable-eng grpcwebproxy which is not recommended unless you require Websocket transport. Even if you do, we advise you to use grpcwebproxy binaries from our fork which contain a few fixes.

gRPC-Web is supported natively by ASP.NET Core.

In all cases, it is highly recommended to use http2, which in turn requires https in all browsers.


Consider the following Protobuf definition:

syntax = "proto3";

package nice_grpc.example;

service ExampleService {
  rpc ExampleUnaryMethod(ExampleRequest) returns (ExampleResponse) {};

message ExampleRequest {
  // ...
message ExampleResponse {
  // ...

After compiling Protobuf file, we can create the client:

When compiling Protobufs using ts-proto:

import {createChannel, createClient} from 'nice-grpc-web';
import {
} from './compiled_proto/example';

const channel = createChannel('http://localhost:8080');

const client: ExampleServiceClient = createClient(

When compiling Protobufs using google-protobuf:

import {createChannel, createClient, Client} from 'nice-grpc';
import {
} from './compiled_proto/example_grpc_pb';

const channel = createChannel('http://localhost:8080');

const client: Client<IExampleService> = createClient(ExampleService, channel);

Further examples use ts-proto.

Call the method:

const response = await client.exampleUnaryMethod(request);

With ts-proto, request is automatically wrapped with fromPartial.

Call options

Each client method accepts CallOptions as an optional second argument, that has type:

type CallOptions = {
   * Request metadata.
  metadata?: Metadata;
   * Signal that cancels the call once aborted.
  signal?: AbortSignal;
   * Called when header is received.
  onHeader?(header: Metadata): void;
   * Called when trailer is received.
  onTrailer?(trailer: Metadata): void;

Call options may be augmented by Middleware.

When creating a client, you may specify default call options per method, or for all methods. This doesn't make much sense for built-in options, but may do for middleware, for example, nice-grpc-client-middleware-deadline:

const client = createClient(ExampleServiceDefinition, channel, {
  '*': {
    // applies for all methods
    deadline: 30_000,
  exampleUnaryMethod: {
    // applies for single method
    deadline: 10_000,

To add default metadata, instead use a middleware that merges it with the metadata passed to the call:

const token = '...';

const client = createClientFactory().use((call, options) =>, {
    metadata: Metadata(options.metadata).set(
      `Bearer ${token}`,

A channel is constructed from an address and optional transport. The following are equivalent:

import {createChannel, FetchTransport} from 'nice-grpc-web';

createChannel('', FetchTransport());

If the port is omitted, it defaults to 80 for http, and 443 for https.

A non-standard WebsocketTransport is also available, that only works with improbable-eng grpcwebproxy and allows to overcome some limitations (see Compatibility). It is still recommended to use FetchTransport whenever possible.

To support older NodeJS versions, we also provide NodeHttpTransport which is based on http and https modules (see Compatibility).


Client can send request metadata and receive response header and trailer:

import {Metadata} from 'nice-grpc-web';

const response = await client.exampleUnaryMethod(request, {
  metadata: Metadata({key: 'value'}),
  onHeader(header: Metadata) {
    // ...
  onTrailer(trailer: Metadata) {
    // ...

Note Most fetch implementations only receive response header when the first chunk of the response body is received. This means that onHeader will be called just before the response (or the first response message in case of server streaming) is received, even if the server sends the header before sending the response.


Client calls may throw gRPC errors represented as ClientError, that contain status code and description.

import {ClientError, Status} from 'nice-grpc-web';
import {ExampleResponse} from './compiled_proto/example';

let response: ExampleResponse | null;

try {
  response = await client.exampleUnaryMethod(request);
} catch (error: unknown) {
  if (error instanceof ClientError && error.code === Status.NOT_FOUND) {
    response = null;
  } else {
    throw error;
Cancelling calls

A client call can be cancelled using AbortSignal.

import {isAbortError} from 'abort-controller-x';

const abortController = new AbortController();

  .exampleUnaryMethod(request, {
    signal: abortController.signal,
  .catch(error => {
    if (isAbortError(error)) {
      // aborted
    } else {
      throw error;

Server streaming

Consider the following Protobuf definition:

service ExampleService {
  rpc ExampleStreamingMethod(ExampleRequest)
    returns (stream ExampleResponse) {};

Client method returns an Async Iterable:

for await (const response of client.exampleStreamingMethod(request)) {
  // ...
Client streaming

Note Most browsers don't support streaming request bodies. See Compatibility for more details.

Given a client streaming method:

service ExampleService {
  rpc ExampleClientStreamingMethod(stream ExampleRequest)
    returns (ExampleResponse) {};

Client method expects an Async Iterable as its first argument:

import {ExampleRequest, DeepPartial} from './compiled_proto/example';

async function* createRequest(): AsyncIterable<DeepPartial<ExampleRequest>> {
  for (let i = 0; i < 10; i++) {
    yield request;

const response = await client.exampleClientStreamingMethod(createRequest());

Client middleware intercepts outgoing calls allowing to:

  • Execute any logic before and after reaching server
  • Modify request metadata
  • Look into request, response and response metadata
  • Send call multiple times for retries or hedging
  • Augment call options type to have own configuration

Client middleware is defined as an Async Generator. The most basic no-op middleware looks like this:

import {ClientMiddlewareCall, CallOptions} from 'nice-grpc-web';

async function* middleware<Request, Response>(
  call: ClientMiddlewareCall<Request, Response>,
  options: CallOptions,
) {
  return yield*, options);

For unary and client streaming methods, the generator yields no items and returns a single response; for server streaming and bidirectional streaming methods, it yields each response and returns void. By doing return yield* we cover both cases. To handle these cases separately, we can write a middleware as follows:

async function* middleware<Request, Response>(
  call: ClientMiddlewareCall<Request, Response>,
  options: CallOptions,
) {
  if (!call.responseStream) {
    const response = yield*, options);

    return response;
  } else {
    for await (const response of, options)) {
      yield response;


To create a client with middleware, use a client factory:

import {createClientFactory} from 'nice-grpc-web';

const client = createClientFactory()
  .create(ExampleService, channel);

A middleware that is attached first, will be invoked last.

You can reuse a single factory to create multiple clients:

const clientFactory = createClientFactory().use(middleware);

const client1 = clientFactory.create(Service1, channel1);
const client2 = clientFactory.create(Service2, channel2);

You can also attach middleware per-client:

const factory = createClientFactory().use(middlewareA);

const client1 = clientFactory.use(middlewareB).create(Service1, channel1);
const client2 = clientFactory.use(middlewareC).create(Service2, channel2);

In the above example, Service1 client gets middlewareA and middlewareB, and Service2 client gets middlewareA and middlewareC.

Example: Logging

Log all calls:

import {
} from 'nice-grpc-web';
import {isAbortError} from 'abort-controller-x';

async function* loggingMiddleware<Request, Response>(
  call: ClientMiddlewareCall<Request, Response>,
  options: CallOptions,
) {
  const {path} = call.method;

  console.log('Client call', path, 'start');

  try {
    const result = yield*, options);

    console.log('Client call', path, 'end: OK');

    return result;
  } catch (error) {
    if (error instanceof ClientError) {
        'Client call',
        `end: ${Status[error.code]}: ${error.details}`,
    } else if (isAbortError(error)) {
      console.log('Client call', path, 'cancel');
    } else {
      console.log('Client call', path, `error: ${error?.stack}`);

    throw error;


This library was tested against:

  • Chrome 71+
  • Firefox 73+
  • Safari 12.1+
  • Android 6+
  • iOS 10.3+
  • NodeJS 16.15+

It might work in older browsers as well.

The library's default FetchTransport requires fetch to be available globally and support for reading a ReadableStream from a Response body. See compatibility table. There is no polyfill for this, so this requirement defines the minimum browser versions. That said, the Websocket transport with grpcwebproxy should work in even older browsers.

Global AbortController is required. A polyfill is available.

This library works in NodeJS 18+ out of the box. It can also be used in NodeJS 16.15 with the --experimental-fetch flag; also client streams require global ReadableStream constructor which can be added manually:

global.ReadableStream ??= require('stream/web').ReadableStream;

It does not work with node-fetch, because it does not support ReadableStream in Response body.

For older NodeJS versions we provide NodeHttpTransport which is based on http and https modules.

Most browsers do not support sending streams in fetch requests. This means that client streaming and bidirectional streaming will not work. The only browser that supports client streams is Chrome 105+ (and other Chromium-based browsers, see compatibility table), and only over http2, which in turn requires https. Client streams work in NodeJS native fetch implementation as well. Note, however, that fetch streams are currently half-duplex, which means that any response data will be buffered until the request stream is sent until the end. This unfortunately makes it impossible to use infinite bidirectional streaming. To overcome this limitation, it is recommended to design your API to use only unary and server streaming methods. If you still need to use client streams in the browser, you can use a Websocket transport with grpcwebproxy.

Browser compatibility is tested with help of BrowserStack.



Last updated on 06 Jun 2024

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