@ -10,90 +10,105 @@ When designing interfaces, break down the common design elements (buttons, form
## Prop Validation
As your app grows it's helpful to ensure that your components are used correctly. We do this by allowing you to specify `propTypes`. `React.PropTypes` exports a range of validators that can be used to make sure the data you receive is valid. When an invalid value is provided for a prop, a warning will be shown in the JavaScript console. Note that for performance reasons `propTypes` is only checked in development mode. Here is an example documenting the different validators provided:
As your app grows it's helpful to ensure that your components are used correctly. We do this by allowing you to specify `propTypes`. `React.PropTypes` exports a range of validators that can be used to make sure the data you receive is valid. When an invalid value is provided for a prop, a warning will be shown in the JavaScript console. Note that for performance reasons `propTypes` is only checked in development mode.
You can assign a special property to a component to declare its `propTypes`:
```javascript
React.createClass({
propTypes: {
// You can declare that a prop is a specific JS primitive. By default, these
// are all optional.
optionalArray: React.PropTypes.array,
optionalBool: React.PropTypes.bool,
optionalFunc: React.PropTypes.func,
optionalNumber: React.PropTypes.number,
optionalObject: React.PropTypes.object,
optionalString: React.PropTypes.string,
optionalSymbol: React.PropTypes.symbol,
// Anything that can be rendered: numbers, strings, elements or an array
// (or fragment) containing these types.
optionalNode: React.PropTypes.node,
// A React element.
optionalElement: React.PropTypes.element,
// You can also declare that a prop is an instance of a class. This uses
With `React.PropTypes.element` you can specify that only a single child can be passed to a component as children.
```javascript
var MyComponent = React.createClass({
propTypes: {
children: React.PropTypes.element.isRequired
},
render: function() {
class MyComponent extends React.Component {
render() {
// This must be exactly one element or it will warn.
var children = this.props.children;
return (
<div>
{this.props.children} // This must be exactly one element or it will warn.
{children}
</div>
);
}
}
});
MyComponent.propTypes = {
children: React.PropTypes.element.isRequired
};
```
## Default Prop Values
@ -122,29 +138,41 @@ var MyComponent = React.createClass({
React lets you define default values for your `props` in a very declarative way:
```javascript
var ComponentWithDefaultProps = React.createClass({
getDefaultProps: function() {
return {
value: 'default value'
};
class Greeting extends React.Component {
render() {
return (
<h1>Hello, {this.props.name}</h1>
);
}
/* ... */
});
}
// Specifies the default values for props:
Greeting.defaultProps = {
name: 'Stranger'
};
// Renders "Hello, Stranger":
ReactDOM.render(
<Greeting/>,
document.getElementById('example')
);
```
The result of `getDefaultProps()` will be cached and used to ensure that `this.props.value` will have a value if it was not specified by the owner component. This allows you to safely just use your props without having to write repetitive and fragile code to handle that yourself.
The `defaultProps` will be used to ensure that `this.props.name` will have a value if it was not specified by the parent component. This allows you to safely just use your props without having to write repetitive and fragile code to handle that yourself.
## Transferring Props: A Shortcut
A common type of React component is one that extends a basic HTML element in a simple way. Often you'll want to copy any HTML attributes passed to your component to the underlying HTML element. To save typing, you can use the JSX _spread_ syntax to achieve this:
```javascript
var CheckLink = React.createClass({
render: function() {
class CheckLink extends React.Component {
render() {
// This takes any props passed to CheckLink and copies them to <a>
Components are the best way to reuse code in React, but sometimes very different components may share some common functionality. These are sometimes called [cross-cutting concerns](https://en.wikipedia.org/wiki/Cross-cutting_concern). React provides `mixins` to solve this problem.
If a component doesn't use local state or lifecycle hooks, you can define it as a function instead of a class:
One common use case is a component wanting to update itself on a time interval. It's easy to use `setInterval()`, but it's important to cancel your interval when you don't need it anymore to save memory. React provides [lifecycle methods](/react/docs/working-with-the-browser.html#component-lifecycle) that let you know when a component is about to be created or destroyed. Let's create a simple mixin that uses these methods to provide an easy `setInterval()` function that will automatically get cleaned up when your component is destroyed.
This simplified component API is intended for components that are pure functions of their props. These components must not retain internal state, do not have backing instances, and do not have the component lifecycle methods. They are pure functional transforms of their input, with zero boilerplate.
However, you may still specify `.propTypes` and `.defaultProps` by setting them as properties on the function, just as you would set them on an ES6 class:
```javascript
function Greeting(props) {
return (
<h1>Hello, {props.name}</h1v>
);
}
Greeting.propTypes = {
name: React.PropTypes.string
};
var TickTock = React.createClass({
mixins: [SetIntervalMixin], // Use the mixin
getInitialState: function() {
return {seconds: 0};
},
componentDidMount: function() {
this.setInterval(this.tick, 1000); // Call a method on the mixin
},
tick: function() {
this.setState({seconds: this.state.seconds + 1});
},
render: function() {
return (
<p>
React has been running for {this.state.seconds} seconds.
</p>
);
}
});
Greeting.defaultProps = {
name: 'John Doe'
};
ReactDOM.render(
<TickTock/>,
<Greetingname="Mădălina"/>,
document.getElementById('example')
);
```
A nice feature of mixins is that if a component is using multiple mixins and several mixins define the same lifecycle method (i.e. several mixins want to do some cleanup when the component is destroyed), all of the lifecycle methods are guaranteed to be called. Methods defined on mixins run in the order mixins were listed, followed by a method call on the component.
>**Note:**
>
> Because stateless functions don't have a backing instance, you can't attach a ref to a stateless function component. Normally this isn't an issue, since stateless functions do not provide an imperative API. Without an imperative API, there isn't much you could do with an instance anyway. However, if a user wants to find the DOM node of a stateless function component, they must wrap the component in a stateful component (eg. ES6 class component) and attach the ref to the stateful wrapper component.
In an ideal world, many of your components would be stateless functions. In the future we plan to make performance optimizations specific to these components by avoiding unnecessary checks and memory allocations.
When you don't need local state or lifecycle hooks in a component, we recommend declaring it with a function. Otherwise, we recommend to use the ES6 class syntax.
## ES6 Classes
## ES6 Classes and React.createClass()
You may also define your React classes as a plain JavaScript class. For example using ES6 class syntax:
Normally you would define a React component as a plain JavaScript class:
The API is similar to `React.createClass` with the exception of `getInitialState`. Instead of providing a separate `getInitialState` method, you set up your own `state` property in the constructor. Just like the return value of `getInitialState`, the value you assign to `this.state` will be used as the initial state for your component.
If you don't use ES6 yet, you may use [`React.createClass`](/react/docs/top-level-api.html#react.createclass) helper instead:
Another difference is that `propTypes` and `defaultProps` are defined as properties on the constructor instead of in the class body.
The API of ES6 classes is similar to [`React.createClass`](/react/docs/top-level-api.html#react.createclass) with a few exceptions.
### Declaring Prop Types and Default Props
Methods follow the same semantics as regular ES6 classes, meaning that they don't automatically bind `this` to the instance. You'll have to explicitly use `.bind(this)` or [arrow functions](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions) `=>`:
With functions and ES6 classes, `propTypes` and `defaultProps` are defined as properties on the components themselves:
```javascript
// You can use bind() to preserve `this`
<divonClick={this.tick.bind(this)}>
class Greeting extends React.Component {
// ...
}
// Or you can use arrow functions
<divonClick={()=> this.tick()}>
Greeting.propTypes = {
name: React.PropTypes.string
};
Greeting.defaultProps = {
name: 'Mary'
};
```
We recommend that you bind your event handlers in the constructor so they are only bound once for every instance:
With `React.createClass()`, you need to define `propTypes` as a property on the passed object, and `getDefaultProps()` as a function on it:
```javascript
constructor(props) {
super(props);
this.state = {count: props.initialCount};
this.tick = this.tick.bind(this);
}
var Greeting = React.createClass({
propTypes: {
name: React.PropTypes.string
},
getDefaultProps: function() {
return {
name: 'Mary'
};
},
// ...
});
```
Now you can use `this.tick` directly as it was bound once in the constructor:
### Setting the Initial State
In ES6 classes, you can define the initial state by assigning `this.state` in the constructor:
```javascript
// It is already bound in the constructor
<divonClick={this.tick}>
class Counter extends React.Component {
constructor(props) {
super(props);
this.state = {count: props.initialCount};
}
// ...
}
```
This is better for performance of your application, especially if you implement [shouldComponentUpdate()](/react/docs/component-specs.html#updating-shouldcomponentupdate) with a [shallow comparison](/react/docs/shallow-compare.html) in the child components.
### No Mixins
With `React.createClass()`, you have to provide a separate `getInitialState` method that returns the initial state:
Unfortunately ES6 launched without any mixin support. Therefore, there is no support for mixins when you use React with ES6 classes. Instead, we're working on making it easier to support such use cases without resorting to mixins.
```javascript
var Counter = React.createClass({
getInitialState: function() {
return {count: props.initialCount};
},
// ...
});
```
## Stateless Functions
### Autobinding
You may also define your React classes as a plain JavaScript function. For example using the stateless function syntax:
In React components declared as ES6 classes, methods follow the same semantics as regular ES6 classes. This means that they don't automatically bind `this` to the instance. You'll have to explicitly use `.bind(this)` in the constructor:
```javascript
function HelloMessage(props) {
return <div>Hello {props.name}</div>;
class SayHello extends React.Component {
constructor(props) {
super(props);
// This line is important!
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
alert('Hello!');
}
render() {
// Because we `this.tick` is bound, we can use it as an event handler.
This simplified component API is intended for components that are pure functions of their props. These components must not retain internal state, do not have backing instances, and do not have the component lifecycle methods. They are pure functional transforms of their input, with zero boilerplate.
This means writing ES6 classes comes with a little more boilerplate code for event handlers, but the upside is slightly better performance in large applications.
If the boilerplate code is too unattractive to you, you may enable the **experimental** [Class Properties](https://babeljs.io/docs/plugins/transform-class-properties/) syntax proposal with Babel:
However, you may still specify `.propTypes` and `.defaultProps` by setting them as properties on the function, just as you would set them on an ES6 class:
> Because stateless functions don't have a backing instance, you can't attach a ref to a stateless function component. Normally this isn't an issue, since stateless functions do not provide an imperative API. Without an imperative API, there isn't much you could do with an instance anyway. However, if a user wants to find the DOM node of a stateless function component, they must wrap the component in a stateful component (eg. ES6 class component) and attach the ref to the stateful wrapper component.
Please note that the syntax above is **experimental** and the syntax may change, or the proposal might not make it into the language.
If you'd rather play it safe, you have a few options:
* Bind methods in the constructor.
* Use arrow functions, e.g. `onClick={(e) => this.handleClick(e)})`.
* Keep using `React.createClass()`.
> NOTE:
### Mixins
>**Note:**
>
>ES6 launched without any mixin support. Therefore, there is no support for mixins when you use React with ES6 classes.
>
>**We also found numerous issues in codebases using mixins, [and don't recommend using them in the new code](/react/blog/2016/07/13/mixins-considered-harmful.html).**
>
> In React v0.14, stateless functional components were not permitted to return `null` or `false` (a workaround is to return a `<noscript />` instead). This was fixed in React v15, and stateless functional components are now permitted to return `null`.
>This section exists only for the reference.
Sometimes very different components may share some common functionality. These are sometimes called [cross-cutting concerns](https://en.wikipedia.org/wiki/Cross-cutting_concern). [`React.createClass`](/react/docs/top-level-api.html#react.createclass) lets you use a legacy `mixins` system for that.
One common use case is a component wanting to update itself on a time interval. It's easy to use `setInterval()`, but it's important to cancel your interval when you don't need it anymore to save memory. React provides [lifecycle methods](/react/docs/working-with-the-browser.html#component-lifecycle) that let you know when a component is about to be created or destroyed. Let's create a simple mixin that uses these methods to provide an easy `setInterval()` function that will automatically get cleaned up when your component is destroyed.
this.setInterval(this.tick, 1000); // Call a method on the mixin
},
tick: function() {
this.setState({seconds: this.state.seconds + 1});
},
render: function() {
return (
<p>
React has been running for {this.state.seconds} seconds.
</p>
);
}
});
ReactDOM.render(
<TickTock/>,
document.getElementById('example')
);
```
In an ideal world, most of your components would be stateless functions because in the future we’ll also be able to make performance optimizations specific to these components by avoiding unnecessary checks and memory allocations. This is the recommended pattern, when possible.
If a component is using multiple mixins and several mixins define the same lifecycle method (i.e. several mixins want to do some cleanup when the component is destroyed), all of the lifecycle methods are guaranteed to be called. Methods defined on mixins run in the order mixins were listed, followed by a method call on the component.
@ -37,7 +37,7 @@ Like all DOM events, the `onChange` prop is supported on all native components a
A **controlled**`<input>` has a `value` prop. Rendering a controlled `<input>` will reflect the value of the `value` prop.
```javascript
render: function() {
render() {
return <inputtype="text"value="Hello!"/>;
}
```
@ -45,13 +45,18 @@ A **controlled** `<input>` has a `value` prop. Rendering a controlled `<input>`
User input will have no effect on the rendered element because React has declared the value to be `Hello!`. To update the value in response to user input, you could use the `onChange` event:
```javascript
getInitialState: function() {
return {value: 'Hello!'};
},
handleChange: function(event) {
class MyForm extends React.Component {
constructor(props) {
super(props);
this.state = {value: 'Hello!'};
this.handleChange = this.handleChange.bind(this);
}
handleChange(event) {
this.setState({value: event.target.value});
},
render: function() {
}
render() {
return (
<input
type="text"
@ -60,12 +65,13 @@ User input will have no effect on the rendered element because React has declare
/>
);
}
}
```
In this example, we are accepting the value provided by the user and updating the `value` prop of the `<input>` component. This pattern makes it easy to implement interfaces that respond to or validate user interactions. For example:
Rafael Angeline
9 years ago
Dan Abramov