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Adding React

This tutorial teaches you how to add webpack to your UPWARD project and use it to create a React application.

This tutorial builds on the project described in the previous Using the TemplateResolver topic.

Install dependencies

Add babel, webpack, and react dependencies to the project:

yarn add @babel/core @babel/preset-env babel-loader webpack webpack-cli @babel/preset-react react react-dom

In addition to installing React, this command installs babel configurations and webpack.

In general, React components are written using ES6(ECMAScript 2015) and JSX syntax for the convenience and ease of readability they provide. Using babel and webpack is a common way to incorporate ES6 and JSX into a React project.

Modify template

Modify the hello-world.mst template to replace the original message with a “root” DOM node for the React application:

{{> templates/open-document}}

  <title>{{ title }}</title>

  {{> templates/open-body}}

-   <b>Hello Template World!</b>
+   <div id="root">Loading...</div>
+   <script defer src="/js/app.js"></script>

  {{> templates/close-document}}

This update renders a loading message in the root DOM and executes the app.js script after the browser parses the HTML document.

Create webpack config

Create a webpack.config.js file to configure webpack behavior:

const path = require('path');

module.exports = {
    mode: 'development',
    entry: './src/hello-world.js',
    output: {
        filename: 'app.js',
        path: path.resolve(__dirname, 'dist')
    module: {
        rules: [
                test: /\.js$/,
                exclude: /node_modules/,
                loader: 'babel-loader'

This configuration file tells webpack to transpile all JavaScript files using babel and bundle src/hello-world.js with its dependencies into dist/app.js.

Create babel config

Create a .babelrc file to configure babel:

  "presets": ["@babel/preset-env","@babel/preset-react"]

This configuration file tells babel what presets to use during JavaScript transpilation. The presets used in this example, @babel/preset-env and @babel/preset-react, are common React development presets.

Create the React application

Create a src directory in your project’s root directory and a hello-world.js file inside that directory with the following content:

import React from 'react';
import ReactDOM from 'react-dom';

class App extends React.Component {
    render() {
        return <h1>Hello React World!</h1>;

ReactDOM.render(<App />, document.getElementById('root'));

This file defines an App React component that returns a “Hello React World!” message wrapped inside h1 tags. It uses the ReactDOM module to inject the content of the application into the “root” DOM element in the document.

Make the application script publicly available

Edit the spec.yml file to add a new URL pattern to check in the ConditionalResolver and a new appScript object.


    resolver: conditional
        - matches: request.url.pathname
          pattern: '^/?$'
          use: helloWorld
        - matches: request.url.pathname
          pattern: '^/hello-world/?$'
          use: helloWorld
+       - matches: request.url.pathname
+         pattern: '^/js/app.js'
+         use: appScript
    default: notFound



+ appScript:
+     inline:
+         status:
+             resolver: inline
+             inline: 200
+         headers:
+             resolver: inline
+             inline:
+                 content-type:
+                     resolver: inline
+                     inline: 'application/javascript'
+         body:
+             resolver: file
+             file:
+                 resolver: inline
+                 inline: './dist/app.js'
+             encoding:
+                 resolver: inline
+                 inline: 'utf-8'

This update uses a FileResolver which instructs the UPWARD server to respond with the contents of dist/app.js when there is a request for the js/app.js path.

Create the bundle and start the server

Create the dist/app.js bundle from src/hello-world.js and start the UPWARD server:

npx webpack && node server.js

When webpack bundles src/hello-world.js into dist/app.js, it includes its dependencies, such as React and ReactDOM.

When you navigate to the server, you will see the React application render the “Hello React World!” message using the App component.