Study notes - Webpack and a proxy for Express

In this example, we will learn how to setup a React-based web app that is served from a local development server, and, at the same time, to have this application to load JSON data from another local server using Express. The logical issue that arises relates to cross-domain access; because your app is first served by the Webpack development server — let's say it comes from the localhost:8080. With that, XMLHTTPRequest access to other server-port is not allowed.

In this proposed solution, we will simply setup a proxy server using Webpack's configuration, which is intended to allow both the development environment and the API server working at the same time.

What are the sources and repositories here for?

The source in this repository is just kept for the sake of referencing the history of the project changes. Throughout this page you will be able to see links to positions in the history of changes.

Making sure certain files are not to be in the version control

First, make sure your .gitignore does not include the ./myProject/node_modules and ./myProject/dist. Dist is where files will be automatically generated by Webpack (and Babel).

myProject/node_modules/
myProject/dist/

Setup myProject

mkdir myProject
cd myProject

Initialize package.json

The setup here assumes NodeJS 8.6.0.

npm init

Install React, React-DOM, Webpack, Webpack-dev-server

And other preset definitions so that Babel can transpile ES2015, and React-based code.

npm install react react-dom --save
npm install webpack webpack-dev-server babel-core babel-loader babel-preset-es2015 babel-preset-react babel-preset-stage-2 --save-dev

Setup scripts in the ./myProject/package.json

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"scripts": {
  "start": "node app.js",
  "babel-start": "npm run build",
  "build": "webpack --mode development && cp src/index.html dist/index.html && webpack-dev-server --mode development --content-base src/ --inline --hot --history-api-fallback",
  "build:prod": "webpack --mode production && cp src/index.html dist/index.html"
},

Preparing your React-based app with Webpack and Babel (for ES6 and React support)

Create your webpack.config.js

var path = require("path");
var DIST_DIR = path.resolve(__dirname, "dist");
var SRC_DIR = path.resolve(__dirname, "src");
var config = {
    entry: SRC_DIR + "/app/index.js",
    output: {
        path: DIST_DIR + "/app",
        filename: "bundle.js",
        publicPath: "/app/"
    },
    module: {
        rules: [
            {
                test: /\.js?/,
                include: SRC_DIR,
                loader: "babel-loader",
                query: {
                    presets: ["react", "es2015", "stage-2"]
                }
            }
        ]
    }
};
module.exports = config;

As you try to execute with "npm run build", in the first time, you should be prompted to install a cli tool.

Do an initial test to check if the Webpack "npm run babel-start" script it properly generating your React code:

npm run babel-start

And test in the browser

http://localhost:8080

Let's make a Node-based Express-based app.js server for serving the API

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'use strict';

const express    = require('express');
const path       = require('path');
const bodyParser = require('body-parser');

const app = express();

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

app.post('/api/test', (req, res, next) => {

  var outputJSON = {
    'status' : null
  }

  console.log("Data received from client: ")
  console.log(req.body);

  res
    .status(200)
    .set('Content-Type', 'application/json')
    .send(JSON.stringify(outputJSON))
    .end();

});

// This cab be used in case you are serving production
//app.use('/', express.static(path.join(__dirname, 'dist')));

// [START listen]
const PORT = process.env.PORT || 8090;
app.listen(process.env.PORT || 8090, () => {
  console.log(`App listening on port ${PORT}`);
  console.log('Press Ctrl+C to quit.');
});
// [END listen]
// [END app]

module.exports = app;

Patching webpack.config.js to have a proxy

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devServer: {
  proxy: {
    "/a/*": {
      target: "http://localhost:8090",
      secure: false,
      rewrite: function(req, options) {
        //you can handle rewrite here if you need to
      }
    },

  }
},

Test your node.js app

node app.js

Setup the new AJAX component to load from the app.js express

npm install axios --save

Add the component to the ./src/app directory

import React, { Component } from 'react';
import axios from 'axios';

class APITester extends Component {

  constructor(props) {
    super(props);
    this.state = {
      loading    : false,
      status     : 'no data yet'
    };
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleSubmit(event) {
    event.preventDefault();

    this.setState({loading:true})

    var data = {
      "argumentToJSON": "foo"
    }

    //     axios.post('/app_send', {data}) // this is like data:data ..
    axios.post('/api/test', data)
        .then(res => {
          if(res.data.status=='ok') {
            this.setState({loading: false, status: 'ok'});
          };
        });

  }

  render() {
      if(!this.state.loading) {
        return (
          <div className="">
            <form onSubmit={this.handleSubmit}>
              <p>
                Result: {this.state.status} <br />
                <input type="submit" value="Call server" />
              </p>
            </form>
          </div>
        );
      } else {
        return (
          <div className="">
              <p>
                loading...
              </p>
          </div>
        );
      }
  }

}

export default APITester;

Update the App.js to include it :

import React, { Component } from 'react';
import APITester from './APITester';

class App extends Component {
  render() {
    return (
      <div className="App">
          <h1 className="App-title">
            Webpack development and API JSON via Proxy
          </h1>

          <APITester />
      </div>
    );
  }
}

export default App;

Run the Dev server

npm run babel-start

Test

http://localhost:8080

In a nutshell:

You are calling your app from localhost:8080
Webpack generates all the output files (index.html, index.js etc in the dist directory)
Webpack will proxy to localhost:8090
Your app.js will answer /api/test

taboca/doc-js-webpack-dev-with-proxy-for-express