react to use some of the notes Hook

   memo

Is a component for rendering of whether reuse, re-rendering to optimize the function of the component behavior, 
in the case where property values are passed unchanged, it will not trigger re-rendering component 

userMemo 
a function logic is executed repeatedly 
consistent syntax and useEffect, but the need to return value, return value can be directly involved in rendering, therefore useMemo is done during rendering