13. JSX for Client Components

All of that routing business was a bit of a diversion from our task at hand: Refactor the client-side component to use JSX

I know that there are 2 ways we can use JSX on the client:

  1. Send JSX down to the browser and use React’s JSXTransformer.js to transform it to JS on the client
  2. Transform the JSX on the server and serve raw JS to the client

Since the ReactJS Starter Kit demonstrates the first option, transforming JSX on the client, we’ll start with that approach.

Before we convert Timestamp.js over to use JSX, let’s introduce the JSX Transformer and ensure that the page still works as-is. Here’s the change to index.jsx.

var React = require('react')
  , HelloWorld = require('./Components/HelloWorld')
  , express = require('express')
  , path = require('path')

var app = express()

  express.static(path.join(path.join(__dirname, '..'),

  express.static(path.join(path.join(__dirname, '..'),

app.get('/', function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'})
  var html = React.renderToString(
        <title>Hello World</title>
        <script src="//fb.me/react-0.13.1.js"></script>
        <script src="//fb.me/JSXTransformer-0.13.1.js"></script>
        <script src="/Components/Timestamp.js" type="text/jsx"></script>
        <HelloWorld from="index.jsx on the server" />
        <div id="reactContainer" />
      <script src="/assets/index.js"></script>


console.log('Server running at http://localhost:1337/')

If we run this, there’s an error in the browser: Uncaught ReferenceError: Timestamp is not defined

Thinking about what’s going on here, we can figure out why this is happening:

  1. The React library is served
  2. The JSXTransformer library is served
  3. The /Components/Timestamp.js file is served, as text/jsx, which queues it up for processing by the JSXTransformer
  4. The /assets/index.js file is served and executed

There’s our problem: The code in /assets/index.js is getting executed, but the JSXTransformer hasn’t yet had an opportunity to process the /Components/Timestamp.js file. There’s an easy fix though: Let’s just change the /assets/index.js script over to also be text/jsx so that the JSXTransformer will be responsible for executing that code, and it will do so after executing the /Components/Timestamp.js code.

<script src="/assets/index.js" type="text/jsx"></script>

That did the trick. The page is working again. While verifying this, I noticed a warning in the browser console though.

You are using the in-browser JSX transformer. Be sure to precompile your JSX for production - http://facebook.github.io/react/docs/tooling-integration.html#jsx

Okay, my gut was right–we’ll want to do this transform on the server at the end of the day. But let’s finish the conversion over to JSX first.

After renaming /Components/Timestamp.js to /Components/Timestamp.jsx, its code gets changed to the following:

var Timestamp = React.createClass({
  getInitialState: function() {
    return { date: "Initial State: " + new Date().toString() }
  render: function() {
    return <div>{this.state.date}</div>

That was only a 1-line change for this component; not bad. We’ll change our index.jsx file to reference it as /Components/Timestamp.jsx now and see if the JSXTransformer does its job…

It did! Refreshing the page, we see that it’s still functioning just like it was before. Huh. That was pretty anti-climactic, wasn’t it? Viewing source, just to make sure the change actually took effect, we can see that sure enough, the following was rendered:

<script src="//fb.me/react-0.13.1.js" data-reactid=".23it8p7ku0w.0.1">

<script src="//fb.me/JSXTransformer-0.13.1.js" data-reactid=".23it8p7ku0w.0.2">

<script src="/Components/Timestamp.jsx" type="text/jsx" data-reactid=".23it8p7ku0w.0.3">

Following the link to /Components/Timestamp.jsx, we also get confirmation that we sent actual JSX code down to the browser and the JSXTransformer component processed it like magic.

Next » Pre-processing Client JSX on the Server