grpc.io/content/en/docs/platforms/web/basics.md

---
title: Basics tutorial
description: A basic tutorial introduction to gRPC-web.
weight: 50
---


This tutorial provides a basic introduction on how to use
gRPC-Web from browsers.

By walking through this example you'll learn how to:

- Define a service in a .proto file.
- Generate client code using the protocol buffer compiler.
- Use the gRPC-Web API to write a simple client for your service.

It assumes a passing familiarity with [protocol
buffers](https://protobuf.dev/overview).

### Why use gRPC and gRPC-Web? {#why-grpc}

With gRPC you can define your service once in a .proto file and implement
clients and servers in any of gRPC's supported languages, which in turn can be
run in environments ranging from servers inside a large data center to your own
tablet - all the complexity of communication between different languages and
environments is handled for you by gRPC. You also get all the advantages of
working with protocol buffers, including efficient serialization, a simple IDL,
and easy interface updating. gRPC-Web lets you access gRPC services built in this
manner from browsers using an idiomatic API.

### Define the Service {#setup}

The first step when creating a gRPC service is to define the service methods
and their request and response message types using protocol buffers. In this
example, we define our `EchoService` in a file called
[`echo.proto`](https://github.com/grpc/grpc-web/blob/0.4.0/net/grpc/gateway/examples/echo/echo.proto).
For more information about protocol buffers and proto3 syntax, please see the
[protobuf documentation][].

```protobuf
message EchoRequest {
  string message = 1;
}

message EchoResponse {
  string message = 1;
}

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

### Implement gRPC Backend Server

Next, we implement our EchoService interface using Node in the backend gRPC
`EchoServer`. This will handle requests from clients. See the file
[`node-server/server.js`](https://github.com/grpc/grpc-web/blob/master/net/grpc/gateway/examples/echo/node-server/server.js)
for details.

You can implement the server in any language supported by gRPC. Please see
the [main page][] for more details.

```js
function doEcho(call, callback) {
  callback(null, {message: call.request.message});
}
```

### Configure the Envoy Proxy

In this example, we will use the [Envoy](https://www.envoyproxy.io/)
proxy to forward the gRPC browser request to the backend server. You can see
the complete config file in
[envoy.yaml](https://github.com/grpc/grpc-web/blob/master/net/grpc/gateway/examples/echo/envoy.yaml)

To forward the gRPC requests to the backend server, we need a block like
this:

```yaml
admin:
  address:
    socket_address: { address: 0.0.0.0, port_value: 9901 }

static_resources:
  listeners:
  - name: listener_0
    address:
      socket_address: { address: 0.0.0.0, port_value: 8080 }
    filter_chains:
    - filters:
      - name: envoy.http_connection_manager
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
          codec_type: auto
          stat_prefix: ingress_http
          route_config:
            name: local_route
            virtual_hosts:
            - name: local_service
              domains: ["*"]
              routes:
              - match: { prefix: "/" }
                route: { cluster: echo_service }
          http_filters:
          - name: envoy.grpc_web
            typed_config:
              "@type": type.googleapis.com/envoy.extensions.filters.http.grpc_web.v3.GrpcWeb
          - name: envoy.filters.http.router
            typed_config:
              "@type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router
  clusters:
  - name: echo_service
    connect_timeout: 0.25s
    type: LOGICAL_DNS
    typed_extension_protocol_options:
      envoy.extensions.upstreams.http.v3.HttpProtocolOptions:
        "@type": type.googleapis.com/envoy.extensions.upstreams.http.v3.HttpProtocolOptions
        explicit_http_config:
          http2_protocol_options: {}
    lb_policy: ROUND_ROBIN
    load_assignment:
      cluster_name: echo_service
      endpoints:
        - lb_endpoints:
          - endpoint:
              address:
                socket_address:
                  address: node-server
                  port_value: 9090
```

You may also need to add some CORS setup to make sure the browser can request
cross-origin content.

In this simple example, the browser makes gRPC requests to port `:8080`. Envoy
forwards the request to the backend gRPC server listening on port `:9090`.

### Generate Protobuf Messages and Service Client Stub

To generate the protobuf message classes from our `echo.proto`, run the
following command:

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

The `import_style` option passed to the `--js_out` flag makes sure the
generated files will have CommonJS style `require()` statements.


To generate the gRPC-Web service client stub, first you need the gRPC-Web
protoc plugin. To compile the plugin `protoc-gen-grpc-web`, you need to run
this from the repo's root directory:

```sh
cd grpc-web
sudo make install-plugin
```

To generate the service client stub file, run this command:

```sh
protoc -I=$DIR echo.proto \
  --grpc-web_out=import_style=commonjs,mode=grpcwebtext:$OUT_DIR
```

In the `--grpc-web_out` param above:
  - `mode` can be `grpcwebtext` (default) or `grpcweb`
  - `import_style` can be `closure` (default) or `commonjs`

Our command generates the client stub, by default, to the file
`echo_grpc_web_pb.js`.

### Write JS Client Code

Now you are ready to write some JS client code. Put this in a `client.js` file.

```js
const {EchoRequest, EchoResponse} = require('./echo_pb.js');
const {EchoServiceClient} = require('./echo_grpc_web_pb.js');

var echoService = new EchoServiceClient('http://localhost:8080');

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

echoService.echo(request, {}, function(err, response) {
  // ...
});
```

You will need a `package.json` file

```json
{
  "name": "grpc-web-commonjs-example",
  "dependencies": {
    "google-protobuf": "^3.6.1",
    "grpc-web": "^0.4.0"
  },
  "devDependencies": {
    "browserify": "^16.2.2",
    "webpack": "^4.16.5",
    "webpack-cli": "^3.1.0"
  }
}
```

### Compile the JS Library

Finally, putting all these together, we can compile all the relevant JS files
into one single JS library that can be used in the browser.

```sh
npm install
npx webpack client.js
```

Now embed `dist/main.js` into your project and see it in action!

[protobuf documentation]:https://protobuf.dev/
[main page]:/docs/