⏱ 0:01est. 7 min

Scheduler

// https://stackoverflow.com/questions/51850236/javascript-scheduler-implementation-using-promises
// https://www.glassdoor.com/Interview/Write-a-scheduler-in-JavaScript-that-accepts-max-number-of-concurrent-tasks-as-a-parameter-and-schedules-tasks-each-task-m-QTN_2553403.htm
// https://leetcode.com/discuss/interview-question/346402/Uber-or-Phone-Screen-or-Design-a-Throttler

let tasks = [
  {
    id: "A",
    isDone: false,
    dependencies: [],
    method: (checkIncompleteTasks, cb) => {
      setTimeout(() => {
        this.isDone = true;
        checkIncompleteTasks("A", cb);
      }, 500);
    },
  },
  {
    id: "B",
    isDone: false,
    dependencies: [],
    method: (checkIncompleteTasks, cb) => {
      setTimeout(() => {
        this.isDone = true;
        checkIncompleteTasks("B", cb);
      }, 502);
    },
  },
  {
    id: "C",
    isDone: false,
    dependencies: ["A", "B"],
    method: (checkIncompleteTasks, cb) => {
      setTimeout(() => {
        this.isDone = true;
        checkIncompleteTasks("C", cb);
      }, 503);
    },
  },
];

const allDoneCallback = () => {
  console.log("all done");
};

const checkIncompleteTasks = (taskName, cb) => {
  tasks.map((t) => {
    if (t.id == taskName) {
      let allDependeniesDone = true;
      if (t.dependencies.length) {
        t.dependencies.forEach((tdId) => {
          tdObj = tasks.filter((tdItem) => tdItem.id == tdId);
          if (!tdObj[0].isDone) {
            allDependeniesDone = false;
          }
        });
      }
      if (allDependeniesDone) {
        t.isDone = true;
      }
    }
    return t;
  });

  runTasks(
    tasks.filter((t) => !t.isDone),
    cb
  );
};

function runTasks(tasks, cb) {
  tasks.map(function (t) {
    t.method(checkIncompleteTasks, cb);
  });
  console.log("tasks", tasks.length);
  if (tasks.length == 0) {
    cb();
  }
}
runTasks(tasks, allDoneCallback);