We launched the React Facebook Page along with the React v0.4 launch. 700 people already liked it to get updated on the project :)

Cross-browser onChange #

Ben Alpert from Khan Academy worked on a cross-browser implementation of onChange event that landed in v0.4. He wrote a blog post explaining the various browser quirks he had to deal with.

First off, what is the input event? If you have an <input> element and want to receive events whenever the value changes, the most obvious thing to do is to listen to the change event. Unfortunately, change fires only after the text field is defocused, rather than on each keystroke. The next obvious choice is the keyup event, which is triggered whenever a key is released. Unfortunately, keyup doesn't catch input that doesn't involve the keyboard (e.g., pasting from the clipboard using the mouse) and only fires once if a key is held down, rather than once per inserted character.

Both keydown and keypress do fire repeatedly when a key is held down, but both fire immediately before the value changes, so to read the new value you have to defer the handler to the next event loop using setTimeout(fn, 0) or similar, which slows down your app. Of course, like keyup, neither keydown nor keypress fires for non-keyboard input events, and all three can fire in cases where the value doesn't change at all (such as when pressing the arrow keys).

Read the full post...

React Samples #

Learning a new library is always easier when you have working examples you can play with. jwh put many of them on his react-samples Github repo.

Some simple examples with Facebook's React framework

• Bootstrap action bar, modal and table #1, #2, #3, #4
• Comments #1, #2
• Data Table #1, #2, #3, #4, #5
• Filter Bar #1, #2, #3, #4, #5
• Fundoo Rating #1
• Line Char: #1, #2
• Multi tabs #1
• Select #1
• Simple Tabs #1, #2, #3, #4
• Toggle #1

React Chosen Wrapper #

Cheng Lou wrote a wrapper for the Chosen input library called react-chosen. It took just 25 lines to be able to use jQuery component as a React one.

React.renderComponent(
  <Chosen noResultsText="No result" value="Harvest" onChange={doSomething}>
    <option value="Facebook">Facebook</option>
    <option value="Harvest">Harvest</option>
  </Chosen>
, document.getElementById('example'));

JSX and ES6 Template Strings #

Domenic Denicola wrote a slide deck about the great applications of ES6 features and one slide shows how we could use Template Strings to compile JSX at run-time without the need for a pre-processing phase.

React Presentation #

Tom Occhino and Jordan Walke, React developers, did a presentation of React at Facebook Seattle's office. Check out the first 25 minutes for the presentation and the remaining 45 for a Q&A. I highly recommend you watching this video.

Docs #

Pete Hunt rewrote the entirety of the docs for v0.4. The goal was to add more explanation about why we built React and what the best practices are.

Guides

• Why React?
• Displaying Data
  • JSX in Depth
  • JSX Gotchas
• Interactivity and Dynamic UIs
• Multiple Components
• Reusable Components
• Forms
• Working With the Browser
  • More About Refs
• Tooling integration
• Reference

Over the past 2 months we've been taking feedback and working hard to make React even better. We fixed some bugs, made some under-the-hood improvements, and added several features that we think will improve the experience developing with React. Today we're proud to announce the availability of React v0.4!

This release could not have happened without the support of our growing community. Since launch day, the community has contributed blog posts, questions to the Google Group, and issues and pull requests on GitHub. We've had contributions ranging from documentation improvements to major changes to React's rendering. We've seen people integrate React into the tools they're using and the products they're building, and we're all very excited to see what our budding community builds next!

React v0.4 has some big changes. We've also restructured the documentation to better communicate how to use React. We've summarized the changes below and linked to documentation where we think it will be especially useful.

When you're ready, go download it!

React #

• Switch from using id attribute to data-reactid to track DOM nodes. This allows you to integrate with other JS and CSS libraries more easily.
• Support for more DOM elements and attributes (e.g., <canvas>)
• Improved server-side rendering APIs. React.renderComponentToString(<component>, callback) allows you to use React on the server and generate markup which can be sent down to the browser.
• prop improvements: validation and default values. Read our blog post for details...
• Support for the key prop, which allows for finer control over reconciliation. Read the docs for details...
• Removed React.autoBind. Read our blog post for details...
• Improvements to forms. We've written wrappers around <input>, <textarea>, <option>, and <select> in order to standardize many inconsistencies in browser implementations. This includes support for defaultValue, and improved implementation of the onChange event, and circuit completion. Read the docs for details...
• We've implemented an improved synthetic event system that conforms to the W3C spec.
• Updates to your component are batched now, which may result in a significantly faster re-render of components. this.setState now takes an optional callback as its second parameter. If you were using onClick={this.setState.bind(this, state)} previously, you'll want to make sure you add a third parameter so that the event is not treated as the callback.

JSX #

• Support for comment nodes <div>{/* this is a comment and won't be rendered */}</div>
• Children are now transformed directly into arguments instead of being wrapped in an array E.g. <div><Component1/><Component2/></div> is transformed into React.DOM.div(null, Component1(null), Component2(null)). Previously this would be transformed into React.DOM.div(null, [Component1(null), Component2(null)]). If you were using React without JSX previously, your code should still work.

react-tools #

• Fixed a number of bugs when transforming directories
• No longer re-write require()s to be relative unless specified

Many of the questions we got following the public launch of React revolved around props, specifically that people wanted to do validation and to make sure their components had sensible defaults.

Validation #

Oftentimes you want to validate your props before you use them. Perhaps you want to ensure they are a specific type. Or maybe you want to restrict your prop to specific values. Or maybe you want to make a specific prop required. This was always possible — you could have written validations in your render or componentWillReceiveProps functions, but that gets clunky fast.

React v0.4 will provide a nice easy way for you to use built-in validators, or to even write your own.

React.createClass({
  propTypes: {
    // An optional string prop named "description".
    description: React.PropTypes.string,

    // A required enum prop named "category".
    category: React.PropTypes.oneOf(['News','Photos']).isRequired,

    // A prop named "dialog" that requires an instance of Dialog.
    dialog: React.PropTypes.instanceOf(Dialog).isRequired
  },
  ...
});

Default Values #

One common pattern we've seen with our React code is to do something like this:

React.createClass({
  render: function() {
    var value = this.props.value || 'default value';
    return <div>{value}</div>;
  }
});

Do this for a few props across a few components and now you have a lot of redundant code. Starting with React v0.4, you can provide default values in a declarative way:

React.createClass({
  getDefaultProps: function() {
    return {
      value: 'default value'
    };
  }
  ...
});

We will use the cached result of this function before each render. We also perform all validations before each render to ensure that you have all of the data you need in the right form before you try to use it.

Both of these features are entirely optional. We've found them to be increasingly valuable at Facebook as our applications grow and evolve, and we hope others find them useful as well.

React reconciliation process appears to be very well suited to implement a text editor with a live preview as people at Khan Academy show us.

Khan Academy #

Ben Kamens explains how Ben Alpert and Joel Burget are promoting React inside of Khan Academy. They now have three projects in the works using React.

Recently two Khan Academy devs dropped into our team chat and said they were gonna use React to write a new feature. They even hinted that we may want to adopt it product-wide.

"The library is only a week old. It's a brand new way of thinking about things. We're the first to use it outside of Facebook. Heck, even the React devs were surprised to hear we're using this in production!!!"

Read the full post...

The best part is the demo of how React reconciliation process makes live editing more user-friendly.

Our renderer, post-React, is on the left. A typical math editor's preview is on the right.

React Snippets #

Over the past several weeks, members of our team, Pete Hunt and Paul O'Shannessy, answered many questions that were asked in the React group. They give a good overview of how to integrate React with other libraries and APIs through the use of Mixins and Lifecycle Methods.

Listening Scroll Event

• JSFiddle: Basically I've given you two mixins. The first lets you react to global scroll events. The second is, IMO, much more useful: it gives you scroll start and scroll end events, which you can use with setState() to create components that react based on whether the user is scrolling or not.

Fade-in Transition

• JSFiddle: Creating a new <FadeInWhenAdded> component and using jQuery .fadeIn() function on the DOM node.
• JSFiddle: Using CSS transition instead.

Socket.IO Integration

• Gist: The big thing to notice is that my component is pretty dumb (it doesn't have to be but that's how I chose to model it). All it does is render itself based on the props that are passed in. renderOrUpdate is where the "magic" happens.
• Gist: This example is doing everything -- including the IO -- inside of a single React component.
• Gist: One pattern that we use at Instagram a lot is to employ separation of concerns and consolidate I/O and state into components higher in the hierarchy to keep the rest of the components mostly stateless and purely display.

Sortable jQuery Plugin Integration

• JSFiddle: Your React component simply render empty divs, and then in componentDidMount() you call React.renderComponent() on each of those divs to set up a new root React tree. Be sure to explicitly unmountAndReleaseReactRootNode() for each component in componentWillUnmount().

Introduction to React Screencast #

Pete Hunt recorded himself implementing a simple <Blink> tag in React.

Snake in React #

Tom Occhino implemented Snake in 150 lines with React.

Check the source on Github

React v0.4 is very close to completion. As we finish it off, we'd like to share with you some of the major changes we've made since v0.3. This is the first of several posts we'll be making over the next week.

What is React.autoBind? #

If you take a look at most of our current examples, you'll see us using React.autoBind for event handlers. This is used in place of Function.prototype.bind. Remember that in JS, function calls are late-bound. That means that if you simply pass a function around, the this used inside won't necessarily be the this you expect. Function.prototype.bind creates a new, properly bound, function so that when called, this is exactly what you expect it to be.

Before we launched React, we would write this:

React.createClass({
  onClick: function(event) {/* do something with this */},
  render: function() {
    return <button onClick={this.onClick.bind(this)} />;
  }
});

We wrote React.autoBind as a way to cache the function creation and save on memory usage. Since render can get called multiple times, if you used this.onClick.bind(this) you would actually create a new function on each pass. With React v0.3 you were able to write this instead:

React.createClass({
  onClick: React.autoBind(function(event) {/* do something with this */}),
  render: function() {
    return <button onClick={this.onClick} />;
  }
});

What's Changing in v0.4? #

After using React.autoBind for a few weeks, we realized that there were very few times that we didn't want that behavior. So we made it the default! Now all methods defined within React.createClass will already be bound to the correct instance.

Starting with v0.4 you can just write this:

React.createClass({
  onClick: function(event) {/* do something with this */},
  render: function() {
    return <button onClick={this.onClick} />;
  }
});

For v0.4 we will simply be making React.autoBind a no-op — it will just return the function you pass to it. Most likely you won't have to change your code to account for this change, though we encourage you to update. We'll publish a migration guide documenting this and other changes that come along with React v0.4.