React.useEffect 未在重新渲染时运行

Question

I have the following component that makes a call to an API (googleSearch()), and using the results passes them to the child component.

The problem is that when the props.date is updated externally, the console.log(search_date) prints the new date however the useEffect just re-uses the old result, and does not make a new API call.

export default function News(props) {

  var searchDate = moment(props.date, "YYYY-MM-DD HH:mm:ss");
  var string_date = searchDate.format("MMMM+DD+YYYY");
  var nice_date = searchDate.format("MMMM DD YYYY");

  const [search_results, updateSearch] = React.useState([]);

  console.log(search_date)


  React.useEffect(() => {
    googleSearch(string_date).then((response) => {
      if (response === "undefined" || response === undefined) {
        updateSearch([])
      } else {
        updateSearch(response.data.items)
      }
    });
  },[]);

  return (
    <React.Fragment>
      <Button>News For {nice_date}</Button>
      <GoogleTable data={search_results} date={props.date} />
    </React.Fragment>
  );

Answer 1

You need to pass string_date into the dependency array on the effect.

React.useEffect(() => {
   ...
}, [string_date])

That makes the effect run when the value of string_date changes, including on mount, and it runs with that new value of string_date

An empty dep array will only run on mount, and not providing an array at all will run the effect on every render