1. voidcallback()

Runs a function asynchronously.

Callbacks registered through this function are always executed in order andare guaranteed to run before other asynchronous events (likeTimer events,or DOM events).

Warning: it is possible to starve the DOM by registering asynchronouscallbacks through this method. For example the following program runsthe callbacks without ever giving the Timer callback a chance to execute:

main() {  Timer.run(() { print("executed"); });  // Will never be executed.  foo() {    scheduleMicrotask(foo);  // Schedules [foo] in front of other events.  }  foo();}

Other resources

• The Event Loop and Dart:Learn how Dart handles the event queue and microtask queue, so you can writebetter asynchronous code with fewer surprises.

Implementation

@pragma('vm:entry-point', 'call')void scheduleMicrotask(void Function() callback) {  _Zone currentZone = Zone._current;  if (identical(_rootZone, currentZone)) {    // No need to bind the callback. We know that the root's scheduleMicrotask    // will be invoked in the root zone.    _rootScheduleMicrotask(null, null, _rootZone, callback);    return;  }  _ZoneFunction implementation = currentZone._scheduleMicrotask;  if (identical(_rootZone, implementation.zone) &&      _rootZone.inSameErrorZone(currentZone)) {    _rootScheduleMicrotask(      null,      null,      currentZone,      currentZone.registerCallback(callback),    );    return;  }  Zone.current.scheduleMicrotask(Zone.current.bindCallbackGuarded(callback));}