使用propTypes进行类型检查

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React文档（十五）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。