July 2, 2019

1152 words 6 mins read



gRPC for Web Clients

repo name grpc/grpc-web
repo link https://github.com/grpc/grpc-web
homepage https://grpc.io
language C++
size (curr.) 750 kB
stars (curr.) 3898
created 2016-06-20
license Other


gRPC-Web provides a JavaScript library that lets browser clients access a gRPC service. You can find out much more about gRPC in its own website.

gRPC-Web is now Generally Available, and considered stable enough for production use.

gRPC-Web clients connect to gRPC services via a special gateway proxy: the current version of the library uses Envoy by default, in which gRPC-Web support is built-in.

In the future, we expect gRPC-Web to be supported in language-specific Web frameworks, such as Python, Java, and Node. See the roadmap doc.

Quick Start Guide: Hello World

You can follow the Hello World Guide to get started with gRPC-Web quickly.

From the guide, you will learn how to

  • Define your service using protocol buffers
  • Implement a simple gRPC Service using NodeJS
  • Configure the Envoy proxy
  • Generate protobuf message classes and client service stub for the client
  • Compile all the JS dependencies into a static library that can be consumed by the browser easily

Advanced Demo: Browser Echo App

You can also try to run a more advanced Echo app from the browser with a streaming example.

From the repo root directory:

$ docker-compose pull
$ docker-compose up

Open a browser tab, and go to:


To shutdown: docker-compose down.

Runtime Library

The gRPC-Web runtime library is available at npm:

$ npm i grpc-web

Code Generator Plugin

You can download the protoc-gen-grpc-web protoc plugin from our release page:

If you don’t already have protoc installed, you will have to download it first from here.

Make sure they are both executable and are discoverable from your PATH.

For example, in MacOS, you can do:

$ sudo mv ~/Downloads/protoc-gen-grpc-web-1.0.7-darwin-x86_64 \
$ chmod +x /usr/local/bin/protoc-gen-grpc-web

Client Configuration Options

Typically, you will run the following command to generate the proto messages and the service client stub from your .proto definitions:

$ protoc -I=$DIR echo.proto \
--js_out=import_style=commonjs:$OUT_DIR \

You can then use Browserify, Webpack, Closure Compiler, etc. to resolve imports at compile time.

Import Style

import_style=closure: The default generated code has Closure goog.require() import style.

import_style=commonjs: The CommonJS style require() is also supported.

import_style=commonjs+dts: (Experimental) In addition to above, a .d.ts typings file will also be generated for the protobuf messages and service stub.

import_style=typescript: (Experimental) The service stub will be generated in TypeScript. See TypeScript Support below for information on how to generate TypeScript files.

Note: The commonjs+dts and typescript styles are only supported by --grpc-web_out=import_style=..., not by --js_out=import_style=....

Wire Format Mode

For more information about the gRPC-Web wire format, please see the specification here.

mode=grpcwebtext: The default generated code sends the payload in the grpc-web-text format.

  • Content-type: application/grpc-web-text
  • Payload are base64-encoded.
  • Both unary and server streaming calls are supported.

mode=grpcweb: A binary protobuf format is also supported.

  • Content-type: application/grpc-web+proto
  • Payload are in the binary protobuf format.
  • Only unary calls are supported for now.

How It Works

Let’s take a look at how gRPC-Web works with a simple example. You can find out how to build, run and explore the example yourself in Build and Run the Echo Example.

1. Define your service

The first step when creating any gRPC service is to define it. Like all gRPC services, gRPC-Web uses protocol buffers to define its RPC service methods and their message request and response types.

message EchoRequest {
  string message = 1;


service EchoService {
  rpc Echo(EchoRequest) returns (EchoResponse);

  rpc ServerStreamingEcho(ServerStreamingEchoRequest)
      returns (stream ServerStreamingEchoResponse);

2. Run the server and proxy

Next you need to have a gRPC server that implements the service interface and a gateway proxy that allows the client to connect to the server. Our example builds a simple Node gRPC backend server and the Envoy proxy.

For the Echo service: see the service implementations.

For the Envoy proxy: see the config yaml file.

3. Write your JS client

Once the server and gateway are up and running, you can start making gRPC calls from the browser!

Create your client

var echoService = new proto.mypackage.EchoServiceClient(

Make a unary RPC call

var request = new proto.mypackage.EchoRequest();
var metadata = {'custom-header-1': 'value1'};
var call = echoService.echo(request, metadata, function(err, response) {
  if (err) {
  } else {
call.on('status', function(status) {

Server-side streaming is supported!

var stream = echoService.serverStreamingEcho(streamRequest, metadata);
stream.on('data', function(response) {
stream.on('status', function(status) {
stream.on('end', function(end) {
  // stream end signal

You can find a more in-depth tutorial from this page.

Setting Deadline

You can set a deadline for your RPC by setting a deadline header. The value should be a Unix timestamp, in milliseconds.

var deadline = new Date();
deadline.setSeconds(deadline.getSeconds() + 1);

client.sayHelloAfterDelay(request, {deadline: deadline.getTime()},
  (err, response) => {
    // err will be populated if the RPC exceeds the deadline

TypeScript Support

The grpc-web module can now be imported as a TypeScript module. This is currently an experimental feature. Any feedback welcome!

When using the protoc-gen-grpc-web protoc plugin, mentioned above, pass in either:

  • import_style=commonjs+dts: existing CommonJS style stub + .d.ts typings
  • import_style=typescript: full TypeScript output

Do not use import_style=typescript for --js_out, it will silently be ignored. Instead you should use --js_out=import_style=commonjs, or --js_out=import_style=commonjs,binary if you are using mode=grpcweb. The --js_out plugin will generate JavaScript code (echo_pb.js), and the -grpc-web_out plugin will generate a TypeScript definition file for it (echo_pb.d.ts). This is a temporary hack until the --js_out supports TypeScript itself.

For example, this is the command you should use to generate TypeScript code using the binary wire format

$ protoc -I=$DIR echo.proto \
--js_out=import_style=commonjs,binary:$OUT_DIR \

It will generate the following files:

  • echo_grpc_web_pb.ts - Generated by --grpc-web_out, contains the TypeScript gRPC-web code.
  • echo_pb.js - Generated by --js_out, contains the JavaScript Protobuf code.
  • echo_pb.d.ts - Generated by --grpc-web_out, contains TypeScript definitions for echo_pb.js.
import * as grpcWeb from 'grpc-web';
import {EchoServiceClient} from './echo_grpc_web_pb';
import {EchoRequest, EchoResponse} from './echo_pb';

const echoService = new EchoServiceClient('http://localhost:8080', null, null);

const request = new EchoRequest();
request.setMessage('Hello World!');

const call = echoService.echo(request, {'custom-header-1': 'value1'},
  (err: grpcWeb.Error, response: EchoResponse) => {
call.on('status', (status: grpcWeb.Status) => {
  // ...

See a full TypeScript example here.

Proxy Interoperability

Multiple proxies supports the gRPC-Web protocol. Currently, the default proxy is Envoy, which supports gRPC-Web out of the box.

$ docker-compose up -d node-server envoy commonjs-client

An alternative is to build Nginx that comes with this repository.

$ docker-compose -f advanced.yml up -d echo-server nginx closure-client

You can also try this gRPC-Web Go Proxy.

$ docker-compose -f advanced.yml up -d node-server grpcwebproxy binary-client


Big thanks to the following contributors for making significant contributions to this project!

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