startDefaultTransitionIndicatorIfNeeded() — react Function Reference

Source Code

packages/react-reconciler/src/ReactFiberRootScheduler.js lines 350–382

function startDefaultTransitionIndicatorIfNeeded() {
  if (!enableDefaultTransitionIndicator) {
    return;
  }
  // Check if we need to start an isomorphic indicator like if an async action
  // was started.
  startIsomorphicDefaultIndicatorIfNeeded();
  // Check all the roots if there are any new indicators needed.
  let root = firstScheduledRoot;
  while (root !== null) {
    if (root.indicatorLanes !== NoLanes && root.pendingIndicator === null) {
      // We have new indicator lanes that requires a loading state. Start the
      // default transition indicator.
      if (hasOngoingIsomorphicIndicator()) {
        // We already have an isomorphic indicator going which means it has to
        // also apply to this root since it implies all roots have the same one.
        // We retain this indicator so that it keeps going until we commit this
        // root.
        root.pendingIndicator = retainIsomorphicIndicator();
      } else {
        try {
          const onDefaultTransitionIndicator =
            root.onDefaultTransitionIndicator;
          root.pendingIndicator = onDefaultTransitionIndicator() || noop;
        } catch (x) {
          root.pendingIndicator = noop;
          reportGlobalError(x);
        }
      }
    }
    root = root.next;
  }
}