reconciler.js

import { updateDomProperties } from "./dom-utils";
import { TEXT_ELEMENT } from "./element";
const ENOUGH_TIME = 1; // we set ours to 1 millisecond.

let workQueue = []; // there is no work initially
let nextUnitOfWork = null; // the nextUnitOfWork is null on initial render.

// the schedule function heere can stand 
// for the scheduleUpdate or the 
// call to render 
// both those calls update the workQueue with a new task.
function schedule(task) {
  // add the task to the workqueue. It will be worked on later.
  workQueue.push(task);
  // request to know when the browser will be pre-occupied.
  // if the browser doesn't support requestIdleCallback
  // react will pollyfill the function but for simplicities sake
  // ill assume your running this on an ever-green browser.
  requestIdleCallback(performWork);
}

function performWork(deadline) {
  loopThroughWork(deadline)
  if (nextUnitOfWork || workQueue.length > 0) {
    // if theres more work to be done. get to know when the browser will be occupied
    // and check if we can perform some work with the timing provided.
    requestIdleCallback(performWork);
  }
}

function loopThroughWork(deadline) {
    while (nextUnitOfWork && deadline.timeRemaining() > ENOUGH_TIME) {
    /**
     * perform unitofwork on a fiber if there's enough time to spare
     * from the browser's end.
     */
    nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
  }
}