reconciler.js

const CLASS_COMPONENT = "class";
// ...code

export function scheduleUpdate(instance, partialState) {
  workQueue.push({
    from: CLASS_COMPONENT, // we know scheduleUpdate came from a class so we have CLASS_COMPONENT here.
    instance: instance, // *this* object
    partialState: partialState // this represents the state that needs to be changed
  });
  requestIdleCallback(performWork);
}