title: Prop value in child component rerender
body: <p>I'm learning react and have 2 questions about rerender behavior. Say a parent component passes a state to a child component as a prop. If the state changes, does the child component gets rerendered twice? I think so since first the state change triggers rerender in parent and parent rerender triggers child rerender, and second prop change in child component also triggers child to rerender. Is my under standing correct?
  My 2nd question is, if the child component gets rerendered twice as I said above, what's the prop value in the 1st rerender? Does it still have the old value since this rerender is not triggered by prop change?</p>