petehunt
12 years ago
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# JSX in Depth |
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JSX is a JavaScript XML syntax transform recommended (but not required) for use |
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with React. |
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## Why JSX? |
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First of all, **don't use JSX if you don't like it!** |
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React works out of the box without JSX. Simply construct your markup using the |
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functions on `React.DOM`. For example, here's how to construct a simple link: |
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```javascript |
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var link = React.DOM.a({href: 'http://facebook.github.io/react'}, 'React'); |
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``` |
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We recommend using JSX for many reasons: |
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- It's easier to visualize the structure of the DOM. |
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- Designers are more comfortable making changes. |
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- It's familiar for those who have used MXML or XAML. |
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## The Transform |
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JSX transforms XML-like syntax into native JavaScript. It turns XML elements and |
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attributes into function calls and objects, respectively. |
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```javascript |
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var Nav; |
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// Input (JSX): |
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var app = <Nav color="blue" />; |
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// Output (JS): |
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var app = Nav({color:'blue'}, null); |
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``` |
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Notice that in order to use `<Nav />`, the `Nav` variable must be in scope. |
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JSX also allows specifying children using XML syntax: |
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```javascript |
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var Nav, Profile; |
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// Input (JSX): |
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var app = <Nav color="blue"><Profile>click</Profile></Nav>; |
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// Output (JS): |
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var app = Nav({color:'blue'}, Profile(null, 'click')); |
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``` |
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Use the [JSX Compiler](/react/jsx-compiler.html) to try out JSX and see how it |
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desugars into native JavaScript. |
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If you want to use JSX, the [Getting Started](getting-started.html) guide shows |
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how to setup compilation. |
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> Note: |
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> |
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> Details about the code transform are given here to increase understanding, but |
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> your code should not rely on these implementation details. |
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## React and JSX |
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React and JSX are independent technologies, but JSX was primarily built with |
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React in mind. The two valid uses of JSX are: |
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- To construct instances of React DOM components (`React.DOM.*`). |
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- To construct instances of composite components created with |
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`React.createClass()`. |
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**React DOM Components** |
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To construct a `<div>` is to create a variable that refers to `React.DOM.div`. |
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```javascript |
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var div = React.DOM.div; |
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var app = <div className="appClass">Hello, React!</div>; |
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``` |
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**React Component Components** |
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To construct an instance of a composite component, create a variable that |
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references the class. |
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```javascript |
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var MyComponent = React.createClass({/*...*/}); |
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var app = <MyComponent someProperty={true} />; |
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``` |
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See [Component Basics](component-basics.html) to learn more about components. |
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> Note: |
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> |
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> Since JSX is JavaScript, identifiers such as `class` and `for` are discouraged |
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> as XML attribute names. Instead, React DOM components expect attributes like |
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> `className` and `htmlFor`, respectively. |
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## DOM Convenience |
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Having to define variables for every type of DOM element can get tedious |
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(e.g. `var div, span, h1, h2, ...`). JSX provides a convenience to address this |
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problem by allowing you to specify a variable in an `@jsx` docblock field. JSX |
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will use that field to find DOM components. |
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```javascript |
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/** |
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* @jsx React.DOM |
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*/ |
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var Nav; |
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// Input (JSX): |
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var tree = <Nav><span /></Nav>; |
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// Output (JS): |
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var tree = Nav(null, React.DOM.span(null, null)); |
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``` |
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> Remember: |
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> |
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> JSX simply transforms elements into function calls and has no notion of the |
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> DOM. The docblock parameter is only a convenience to resolve the most commonly |
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> used elements. In general, JSX has no notion of the DOM. |
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## JavaScript Expressions |
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#### Attribute Expressions |
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To use a JavaScript expression as an attribute value, wrap the expression in a |
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pair of curly braces (`{}`) instead of quotes (`""`). |
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```javascript |
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// Input (JSX): |
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var person = <Person name={window.isLoggedIn ? window.name : ''} />; |
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// Output (JS): |
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var person = Person({name: window.isLoggedIn ? window.name : ''}); |
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``` |
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#### Child Expressions |
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Likewise, JavaScript expressions may be used to express children: |
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```javascript |
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// Input (JSX): |
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var content = <Container>{window.isLoggedIn ? <Nav /> : <Login />}</Container>; |
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// Output (JS): |
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var content = Container(null, window.isLoggedIn ? Nav(null, null) : Login(null, null)); |
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``` |
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## Tooling |
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Beyond the compilation step, JSX does not require any special tools. |
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- Many editors already include reasonable support for JSX (Vim, Emacs js2-mode). |
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- Linting provides accurate line numbers after compiling without sourcemaps. |
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- Elements use standard scoping so linters can find usage of out-of-scope |
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components. |
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## Prior Work |
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JSX is similar to several other JavaScript embedded XML language |
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proposals/projects. Some of the features of JSX that distinguish it from similar |
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efforts include: |
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- JSX is a simple syntactic transform. |
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- JSX neither provides nor requires a runtime library. |
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- JSX does not alter or add to the semantics of JavaScript. |
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@ -0,0 +1,59 @@ |
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# Handling User Input |
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You've already [learned how to display data](./02-displaying-data.html) with React. Now let's look at how to make our UIs interactive. |
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## A simple example |
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```javascript |
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/** @jsx React.DOM */ |
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var LikeButton = React.createClass({ |
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getInitialState: function() { |
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return {liked: false}; |
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}, |
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handleClick: function(event) { |
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this.setState({liked: !this.state.liked}); |
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}, |
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render: function() { |
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var text = this.state.liked ? 'like' : 'unlike'; |
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return ( |
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<p onClick={this.handleClick}> |
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You {text} this. Click to toggle. |
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</p> |
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); |
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} |
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}); |
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React.renderComponent( |
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<LikeButton />, |
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document.getElementById('example') |
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); |
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``` |
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## Event handling and synthetic events |
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With React you simply pass your event handler as a camelCased prop similar to how you'd do it in normal HTML. React ensures that all events behave identically in IE8 and above by implementing a synthetic event system. That is, React knows how to bubble and capture events according to the spec, and the events passed to your event handler are guaranteed to be consistent with [the W3C spec](http://www.w3.org/TR/DOM-Level-3-Events/), regardless of which browser you're using. |
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## Under the hood: autoBind and event delegation |
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Under the hood React does a few things to keep your code performant and easy to understand. |
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**Autobinding.** Every method is automatically bound to its component instance. React caches the bound method such that it's extremely CPU and memory efficient. It's also less typing! |
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**Event delegation.** React doesn't actually attach event handlers to the nodes themselves. When React starts up, it starts listening for all events at the top level using a single event listener. When a component is mounted or unmounted, the event handlers are simply added or removed from a fast internal event mapping. When the event occurs, React knows how to dispatch it using this mapping. When there are no event handlers left in the mapping, React's event handlers are simple no-ops |
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## How state works |
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A common way to inform React of a data change is by calling `setState(data, callback)`. This method merges `data` into `this.state` and re-renders the component. When the component finishes re-rendering, the optional `callback` is called. Most of the time you'll never need to provide a `callback` since state tends to be so minimal. |
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## What components should have state? |
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Most of your components should simply take some data from `props` and render it. However, sometimes you need to respond to user input, a server request or the passage of time. For this you use state. |
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**Try to keep as many of your components as possible stateless.** By doing this you'll isolate the state to its most logical place and minimize redundancy, making it easier to reason about your application. |
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A common pattern is to create several stateless components that just render data, and have a stateful component above them in the hierarchy that passes its state to its children via `props`. The stateful component encapsulates all of the interaction logic, while the stateless components take care of rendering data in a declarative way. |
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## What should go in state? |
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**`this.state` should contain any data that the component's event handlers will change that should trigger a UI update.** In real apps this data tends to be very small and JSON-serializable. When building a stateful component, think about the minimal possible representation of its state, and only store those properties in `this.state`. Inside of `render()` simply compute any other information you need based on this state. You'll find that thinking about and writing applications in this way tends to lead to the most correct application, since adding redundant or computed values to state means that you need to explicitly keep them in sync rather than rely on React computing them for you. |
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