在道具准备好之前阻止 React 组件渲染

Question

I'm a React noobie, or midbie. This component is mappping an empty posts array coming as a prop from its parent.

How do I make it wait until the props having finished updating before doing the return() where the mapping happens?

I think I need to use useEffect but I'm not sure the syntax.

const Timeline = props => {
  console.log(props.posts.length); // logs twice: initially 0, then 6 a microsecond later.

  useEffefct(()=>{
    // if props is all done and ready, goto return statement
  }, [props]);

  return (
    <>
      <CreatePost />
      <div className="post-list">
        {props.posts.map((post, i) => ( // this maps the initial empty array
          <Post key={i} post={post} />
        ))}
      </div>
    </>
  );
};

export default Timeline;

Answer 1

You can also use an inline condition to prevent mapping if array is not filled yet.

{(props.posts.length > 0) && props.posts.map((post, i) => (
   <Post key={i} post={post} />
))}