Markdium-用 Substrate Front-end Template 轻松打造你的 React 应用

Markdium-javascript.js

useEffect(() => {
  let unsubscribe;
  api.query.templateModule.something(newValue => {
    // The storage value is an Option<u32>
    // So we have to check whether it is None first
    // There is also unwrapOr
    if (newValue.isNone) {
      setCurrentValue('<None>');
    } else {
      setCurrentValue(newValue.unwrap().toNumber());
    }
  }).then(unsub => {
    unsubscribe = unsub;
  })
    .catch(console.error);

  return () => unsubscribe && unsubscribe();
}, [api.query.templateModule]);