React版本：15.4.2
**翻譯：xiyoki **

隨著應(yīng)用程序的成長(zhǎng)，你可以通過(guò)typechecking捕捉很多bug。對(duì)于某些應(yīng)用程序，你可以使用Javascript擴(kuò)展（如Flow或TypeScript）來(lái)對(duì)整個(gè)應(yīng)用程序進(jìn)行類型檢查。但是即使你不使用這些，React也有一些內(nèi)置的typechecking能力。要在組件的props上運(yùn)行typechecking，可以指定特殊的propTypes屬性：

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

Greeting.propTypes = {
  name: React.PropTypes.string
};

React.PropTypes導(dǎo)出一系列驗(yàn)證器，可用于確保接收的數(shù)據(jù)有效。在這個(gè)例子中，我們正在使用React.PropTypes.string。當(dāng)為prop提供無(wú)效值時(shí)，Javascript控制臺(tái)中將顯示警告。出于性能原因，propTypes僅在開發(fā)模式下檢查。

React.PropTypes

這里是一個(gè)示例，提供了不同的驗(yàn)證器：

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.'
      );
    }
  })
};

Requiring Single Child（需要單獨(dú)的child）

對(duì)于React.PropTypes.element，你可以指定只有一個(gè)單獨(dú)的child作為children被傳遞給組件。

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
};

Default Prop Values（默認(rèn)的Prop值）

你可以為你的props定義默認(rèn)的值，通過(guò)將特殊的defaultProps屬性賦給props：

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將被用于確保this.props.name有一個(gè)值，如果它的值不是由父組件指定。當(dāng)defaultProps被處理后，propTypes類型檢查將會(huì)進(jìn)行，所以類型檢查也將適用于defaultProps。