State Hook

1、State Hook Let function components also have state state , And read and write the state data

2、 grammar ：const[xxx,setXxx]=React.useState(initValue)

3、useState() explain ：

• Parameters ： The first initialization of the specified value in the internal cache
• Return value ： contain 2 Array of elements , The first 1 Are current status values within , The first 2 A function to update the state value

4、setXxx()2 Species writing ：

• setXxx(newValue)： The parameter is a non functional value , Directly specify the new state value , It is used internally to override the original state value
• setXxx(value => newValue)： The number of parameters is , Receive the original status value , Returns the new status value , It is used internally to override the original state value