此文章是翻译Typechecking With PropTypes这篇React（版本v16.2.0）官方文档。

Typechecking With PropTypes

注意：

React.PropTypes 从React v15.5 版本已经移入一个不同的包。请使用prop-types库替代

随着你的应用的增大， 你可以通过类型检测（typechecking）捕获许多bugs。对于一些应用，你可以使用JavaScript 扩展例如Flow或者TypeScript 去检测你的整个应用。但是即使你不使用这些，在React 有一些内置的类型检测能力。为了能够在组件的props 上运行类型检测，你需要配置特殊的propTypes 属性：

  1. import PropTypes from 'prop-types';
  3. class Greeting extends React.Component {
  4.   render() {
  5.     return (
  6.       <h1>Hello , {this.props.name}</h1>
  7.     );
  8.   }
  9. }
  11. Greeting.propTypes = {
  12.   name : PropTypes.string
  13. };

PropTypes 导出一系列的验证器（validator）可以用来确认你收到有效的数据。在这个例子中，我们使用PropTypes.string。当一个无效的值被提供给prop，一个警告就会在JavaScript console 中显示。为了性能原因，propTypes 只在开发模式进行验证。

PropTypes

这有一个例子展示如何使用不同验证器：

  1. import PropTypes from 'prop-types';
  3. MyComponent.propTypes = {
  4.   // You can declare that a prop is a specific JS primitive. By default, these
  5.   // are all optional.
  6.   optionalArray: PropTypes.array,
  7.   optionalBool: PropTypes.bool,
  8.   optionalFunc: PropTypes.func,
  9.   optionalNumber: PropTypes.number,
  10.   optionalObject: PropTypes.object,
  11.   optionalString: PropTypes.string,
  12.   optionalSymbol: PropTypes.symbol,
  14.   // Anything that can be rendered: numbers, strings, elements or an array
  15.   // (or fragment) containing these types.
  16.   optionalNode: PropTypes.node,
  18.   // A React element.
  19.   optionalElement: PropTypes.element,
  21.   // You can also declare that a prop is an instance of a class. This uses
  22.   // JS's instanceof operator.
  23.   optionalMessage: PropTypes.instanceOf(Message),
  25.   // You can ensure that your prop is limited to specific values by treating
  26.   // it as an enum.
  27.   optionalEnum: PropTypes.oneOf(['News', 'Photos']),
  29.   // An object that could be one of many types
  30.   optionalUnion: PropTypes.oneOfType([
  31.     PropTypes.string,
  32.     PropTypes.number,
  33.     PropTypes.instanceOf(Message)
  34.   ]),
  36.   // An array of a certain type
  37.   optionalArrayOf: PropTypes.arrayOf(PropTypes.number),
  39.   // An object with property values of a certain type
  40.   optionalObjectOf: PropTypes.objectOf(PropTypes.number),
  42.   // An object taking on a particular shape
  43.   optionalObjectWithShape: PropTypes.shape({
  44.     color: PropTypes.string,
  45.     fontSize: PropTypes.number
  46.   }),
  48.   // You can chain any of the above with `isRequired` to make sure a warning
  49.   // is shown if the prop isn't provided.
  50.   requiredFunc: PropTypes.func.isRequired,
  52.   // A value of any data type
  53.   requiredAny: PropTypes.any.isRequired,
  55.   // You can also specify a custom validator. It should return an Error
  56.   // object if the validation fails. Don't `console.warn` or throw, as this
  57.   // won't work inside `oneOfType`.
  58.   customProp: function(props, propName, componentName) {
  59.     if (!/matchme/.test(props[propName])) {
  60.       return new Error(
  61.         'Invalid prop `' + propName + '` supplied to' +
  62.         ' `' + componentName + '`. Validation failed.'
  63.       );
  64.     }
  65.   },
  67.   // You can also supply a custom validator to `arrayOf` and `objectOf`.
  68.   // It should return an Error object if the validation fails. The validator
  69.   // will be called for each key in the array or object. The first two
  70.   // arguments of the validator are the array or object itself, and the
  71.   // current item's key.
  72.   customArrayProp: PropTypes.arrayOf(function(propValue, key, componentName, location, propFullName) {
  73.     if (!/matchme/.test(propValue[key])) {
  74.       return new Error(
  75.         'Invalid prop `' + propFullName + '` supplied to' +
  76.         ' `' + componentName + '`. Validation failed.'
  77.       );
  78.     }
  79.   })
  80. };

Requiring Single Children

使用React.PropTypes.element 你可以配置仅允许单个子节点传给组件：

  1. import PropTypes from 'prop-types';
  3. class MyComponent extends React.Component {
  4.   render() {
  5.     // This must be exactly one element or it will warn.
  6.     const children = this.props.children;
  7.     return (
  8.       <div>
  9.         {children}
  10.       </div>
  11.     );
  12.   }
  13. }
  15. MyComponent.PropTypes = {
  16.   children: PropTypes.element.isRequired
  17. };

Default Prop Values

通过为你的props 配置一个特殊的defaultProps 属性来定义一个默认值：

  1. class Greeting extends React.Component {
  2.   render() {
  3.     return (
  4.       <h1>Hello , {this.props.name}</h1>
  5.     );
  6.   }
  7. }
  9. // Specifies the default values for props:
  10. Greeting.defaultProps = {
  11.   name: 'Stranger'
  12. }
  14. // Renders "Hello, Stranger"
  15. ReactDOM.render(
  16.   <Greeting />,
  17.   document.getElementById('root')
  18. )

如果你正在用像transform-class-properties Babel 转换器，你也可以在React 组件类中声明defaultProps 作为静态属性。这个语法还没有最终通过，在浏览器中需要一步编译工作。更多信息，查看class fields proposal。

  1. class Greeting extends React.Component {
  2.   static defaultProps = {
  3.     name: 'stranger'
  4.   }
  6.   render() {
  7.     return (
  8.       <div>Hello, {this.props.name}</div>
  9.     )
  10.   }
  11. }

这个defaultProps 将会确认这个this.props.name 有值即使它没有被父组件配置。这个propType 将在defaultProps 被解析之后进行类型检测，所以类型检测也可用在defaultProps 上。