官方文档（https://reactjs.org/docs/react-component.html#unsafe_componentwillreceiveprops）有一句是这样说的：
Using this lifecycle method often leads to bugs and inconsistencies, and for that reason it is going to be deprecated in the future.
到底有哪些bugs和inconsistencies呢？文档里面有这样一句话：
Note that if a parent component causes your component to re-render, this method will be called even if props have not changed. Make sure to compare the current and next values if you only want to handle changes.
即：只要父组件引起了你的组件的 重新render，你的组件就会触发componentWillReceiveProps方法，即使你组件接收的props没有发生任何变化。
希望大家补充的更深刻。。。