20210831 - React - Cannot read property 'map' of undefined

今天遇到了这个error

Solutions:

React - Cannot read property ‘map’ of undefined

好吧，其实是我在App中给Person传递property的时候，property的名字少写了一个字母。。。而且VSCode竟然也给了我错误的名字提示。。。

另外在做2.14 weather的练习时也遇到了这种’Can’t read xxx of undefined’情况。

一个解释：

You should know when data hasn’t been loaded yet and you cannot render. Usually a simple if and return null is enough in that case

if (example == null) {
return null
}