petehunt
12 years ago
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# JSX gotchas |
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JSX looks like HTML but there are some important differences you may run into. |
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## Whitespace removal |
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JSX doesn't follow the same whitespace elimination rules as HTML. JSX removes all whitespace between two curly braces expressions. If you want to have whitespace, simply add `{' '}`. |
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```javascript |
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<div>{this.props.name} {' '} {this.props.surname}</div> |
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``` |
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Follow [Issue #65](https://github.com/facebook/react/issues/65) for discussion on this behavior. |
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## HTML Entities |
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You can insert HTML entities within literal text in JSX: |
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```javascript |
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<div>First · Second</div> |
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``` |
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If you want to display an HTML entity within dynamic content, you will run into double escaping issues as React escapes all the strings you are displaying in order to prevent a wide range of XSS attacks by default. |
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```javascript |
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// Bad: It displays "First · Second" |
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<div>{'First · Second'}</div> |
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``` |
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There are various ways to work-around this issue. The easiest one is to write unicode character directly in Javascript. You need to make sure that the file is saved as UTF-8 and that the proper UTF-8 directives are set so the browser will display it correctly. |
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```javascript |
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<div>{'First · Second'}</div> |
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``` |
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A safer alternative is to find the [unicode number corresponding to the entity](http://www.fileformat.info/info/unicode/char/b7/index.htm) and use it inside of a JavaScript string. |
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```javascript |
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<div>{'First \u00b7 Second'}</div> |
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<div>{'First ' + String.fromCharCode(183) + ' Second'}</div> |
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``` |
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You can use mixed arrays with strings and JSX elements. |
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```javascript |
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<div>{['First ', <span>·</span>, ' Second']}</div> |
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``` |
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As a last resort, you always have the ability to insert raw HTML. |
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```javascript |
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<div dangerouslySetInnerHTML={{'{{'}}__html: 'First · Second'}} /> |
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``` |
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## Comments |
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JSX supports both single-line and multi-line JavaScript comments within a tag declaration: |
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```javascript |
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<div // This is a single-line comment: |
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/* |
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And a multi-line |
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comment |
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*/ |
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/> |
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``` |
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As of React 0.3, there is no good way to insert comments within the children section. [Issue #82](https://github.com/facebook/react/issues/82) is tracking progress to enable the following: |
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```javascript |
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// Note: This is not implemented yet! |
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<div> |
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{/* This is a comment */} |
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</div> |
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``` |
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## Custom HTML Attributes |
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If you pass properties to native HTML elements that do not exist in the HTML specification, React will not render them. If you want to use a custom attribute, you should prefix it with `data-`. |
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```javascript |
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<div data-custom-attribute="foo" /> |
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``` |
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[Web Accessibility](http://www.w3.org/WAI/intro/aria) attributes starting with `aria-` will be rendered properly. |
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```javascript |
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<div aria-hidden={true} /> |
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``` |
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# Reference |
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## API |
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### React |
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`React` is the entry point to the React framework. If you're using one of the prebuilt packages it's available as a global; if you're using CommonJS modules you can `require()` it. |
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#### React.DOM |
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`React.DOM` provides all of the standard HTML tags needed to build a React app. You generally don't use it directly; instead, just include it as part of the `/** @jsx React.DOM */` docblock. |
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#### React.initializeTouchEvents |
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```javascript |
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initializeTouchEvents(boolean shouldUseTouch) |
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``` |
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Configure React's event system to handle touch events on mobile devices. |
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#### React.createClass |
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```javascript |
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function createClass(object specification) |
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``` |
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Creates a component given a specification. A component implements a `render` method which returns **one single** child. That child may have an arbitrarily deep child structure. One thing that makes components different than a standard prototypal classes is that you don't need to call new on them. They are convenience wrappers that construct backing instances (via new) for you. |
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#### React.renderComponent |
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```javascript |
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ReactComponent renderComponent(ReactComponent container, DOMElement container) |
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``` |
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Renders a React component into the DOM in the supplied `container`. |
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If the React component was previously rendered into `container`, this will perform an update on it and only mutate the DOM as necessary to reflect the latest React component. |
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#### React.unmountAndReleaseReactRootNode |
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```javascript |
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unmountAndReleaseReactRootNode(DOMElement container) |
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``` |
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Remove a mounted React component from the DOM and clean up its event handlers and state. |
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#### React.renderComponentToString |
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```javascript |
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renderComponentToString(ReactComponent component, function callback) |
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``` |
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Render a component to its initial HTML. This should only be used on the server. React will call `callback` with an HTML string when the markup is ready. You can use this method to create static site generators, or you can generate HTML on the server and send it down to have a very fast initial page load. If you call `React.renderComponent()` on a node that already has this server-rendered markup, React will preserve it and only attach event handlers, allowing you to have a very performant first-load experience. |
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### AbstractEvent |
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Your event handlers will be passed instances of `AbstractEvent`, a cross-browser wrapper around the browser's native event. It has the same interface as the browser's native event (such as `stopPropagation()` and `preventDefault()`) except they work exactly the same across all browsers. |
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If you find that you need the underlying browser event for some reason, simply use the `nativeEvent` attribute to get it. |
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### ReactComponent |
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Component classses created by `createClass()` return instances of `ReactComponent` when called. Most of the time when you're using React you're either creating or consuming `ReactComponent`s. |
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#### getDOMNode |
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```javascript |
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DOMElement getDOMNode() |
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``` |
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If this component has been mounted into the DOM, this returns the corresponding native browser DOM element. This method is useful for reading values out of the DOM, such as form field values and performing DOM measurements. |
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#### setProps |
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```javascript |
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setProps(object nextProps) |
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``` |
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When you're integrating with an external JavaScript application you may want to signal a change to a React component rendered with `renderComponent()`. Simply call `setProps()` to change its properties and trigger a re-render. |
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**Note:** This method can only be called on a root-level component. That is, it's only available on the component passed directly to `renderComponent()` and none of its children. If you're inclined to use `setProps()` on a child component, instead take advantage of reactive updates and pass the new prop to the child component when it's created in `render()`. |
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#### replaceProps |
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```javascript |
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replaceProps(object nextProps) |
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``` |
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Like `setProps()` but deletes any pre-existing props that are not in nextProps. |
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#### transferPropsTo |
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```javascript |
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ReactComponent transferPropsTo(ReactComponent targetComponent) |
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``` |
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Transfer properties from this component to a target component that have not already been set on the target component. This is usually used to pass down properties to the returned root component. `targetComponent`, now updated with some new props is returned as a convenience. |
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#### setState |
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```javascript |
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setState(object nextState[, function callback]) |
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``` |
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Merges nextState with the current state. This is the primary method you use to trigger UI updates from event handlers and server request callbacks. In addition, you can supply an optional callback function that is executed once `setState` is completed. |
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**Note:** *NEVER* mutate `this.state` directly. As calling `setState()` afterwards may replace the mutation you made. Treat `this.state` as if it were immutable. |
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**Note:** `setState()` does not immediately mutate `this.state` but creates a pending state transition. Accessing `this.state` after calling this method can potentially return the existing value. |
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**Note**: There is no guarantee of synchronous operation of calls to `setState` and calls may be batched for performance gains. |
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#### replaceState |
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```javascript |
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replaceState(object nextState[, function callback]) |
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``` |
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Like `setState()` but deletes any pre-existing state keys that are not in nextState. |
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#### forceUpdate() |
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```javascript |
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forceUpdate([function callback]) |
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``` |
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If your `render()` method reads from something other than `this.props` or `this.state` you'll need to tell React when it needs to re-run `render()`. Use `forceUpdate()` to cause React to automatically re-render. This will cause `render()` to be called on the component and all of its children but React will only update the DOM if the markup changes. |
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Normally you should try to avoid all uses of `forceUpdate()` and only read from `this.props` and `this.state` in `render()`. This makes your application much simpler and more efficient. |
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**Note**: There is no guarantee of synchronous operation of calls to `forceUpdate` and calls may be batched for performance gains. |
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#### Lifecycle methods |
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```javascript |
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object getInitialState() |
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componentWillMount() |
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componentDidMount(DOMElement domNode) |
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componentWillReceiveProps(object nextProps) |
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boolean shouldComponentUpdate(object nextProps, object nextState) |
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componentWillUpdate(object nextProps, object nextState) |
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ReactComponent render() |
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componentDidUpdate(object prevProps, object prevState, DOMElement domNode) |
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componentWillUnmount() |
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``` |
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See the [working with the browser](./07-working-with-the-browser.md) documentation for more details on these lifecycle methods. |
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## DOM differences |
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React has implemented a browser-independent events and DOM system for performance and cross-browser compatibility reasons. We took the opportunity to clean up a few rough edges in browser DOM implementations. |
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* All events (including submit) bubble correctly per the W3C spec |
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* All event objects conform to the W3C spec |
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* All DOM properties and attributes (including event handlers) should be camelCased to be consistent with standard JavaScript style. We intentionally break with the spec here, since the spec is inconsistent. |
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* `onChange` behaves as you would expect it to: whenever a form field is changed this event is fired rather than inconsistently on blur. We intentionally break from existing browser behavior because `onChange` is a misnomer for its behavior and React relies on this event to react to user input in real time. |
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