使用propTypes进行类型检查

随着你的应用的开发，你会使用类型检查的方法来捕获很多bug。对于一些应用，你可以使用js扩展就像Flow或者TypeScript去对整个应用进行类型检查。但是即使你不是用这些扩展语言，React也有一些内置的类型检查功能。在props上运行类型检查，你可以指派特殊的propTypes属性：

class Greeting extends React.Component {  render() {    return (      <h1>Hello, {this.props.name}</h1>    );  }}Greeting.propTypes = {  name: React.PropTypes.string};

React.PropTypes导出一系列验证工具可以确保你接收到的数据是有效的。在这个例子里，我们使用React.PropTypes.string。当一个无效的值被作为prop提供时，一个警告就会出现在js控制台里。因为性能的原因，propTypes只是在开发环境里来使用。

React.PropTypes

下面是一个不同验证的例子：

MyComponent.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  // JS's instanceof operator.  optionalMessage: React.PropTypes.instanceOf(Message),  // You can ensure that your prop is limited to specific values by treating  // it as an enum.  optionalEnum: React.PropTypes.oneOf(['News', 'Photos']),  // An object that could be one of many types  optionalUnion: React.PropTypes.oneOfType([    React.PropTypes.string,    React.PropTypes.number,    React.PropTypes.instanceOf(Message)  ]),  // An array of a certain type  optionalArrayOf: React.PropTypes.arrayOf(React.PropTypes.number),  // An object with property values of a certain type  optionalObjectOf: React.PropTypes.objectOf(React.PropTypes.number),  // An object taking on a particular shape  optionalObjectWithShape: React.PropTypes.shape({    color: React.PropTypes.string,    fontSize: React.PropTypes.number  }),  // You can chain any of the above with `isRequired` to make sure a warning  // is shown if the prop isn't provided.  requiredFunc: React.PropTypes.func.isRequired,  // A value of any data type  requiredAny: React.PropTypes.any.isRequired,  // You can also specify a custom validator. It should return an Error  // object if the validation fails. Don't `console.warn` or throw, as this  // won't work inside `oneOfType`.  customProp: function(props, propName, componentName) {    if (!/matchme/.test(props[propName])) {      return new Error(        'Invalid prop `' + propName + '` supplied to' +        ' `' + componentName + '`. Validation failed.'      );    }  },  // You can also supply a custom validator to `arrayOf` and `objectOf`.  // It should return an Error object if the validation fails. The validator  // will be called for each key in the array or object. The first two  // arguments of the validator are the array or object itself, and the  // current item's key.  customArrayProp: React.PropTypes.arrayOf(function(propValue, key, componentName, location, propFullName) {    if (!/matchme/.test(propValue[key])) {      return new Error(        'Invalid prop `' + propFullName + '` supplied to' +        ' `' + componentName + '`. Validation failed.'      );    }  })};

要求单个子元素

通过React.PropTypes.element你可以指定只能有一个子元素被作为children传递给一个组件。

class MyComponent extends React.Component {  render() {    // This must be exactly one element or it will warn.    const children = this.props.children;    return (      <div>        {children}      </div>    );  }}MyComponent.propTypes = {  children: React.PropTypes.element.isRequired};

默认prop值

你可以定义props的默认值通过分配特殊的defaultProps属性：

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'));

defaultProps会确保this.props.name将会有一个值如果它没有被父组件所指定。propTypes类型检查会在defaultProps解决了之后执行，因此defaultProps也会应用。