function delay(ms) { return new Promise(resolve => setTimeout(resolve, ms)) }

这个 JavaScript 函数 `delay` 定义了一个返回 Promise 的辅助函数，它的作用是在指定的时间 (`ms`) 后自动解析（resolve）Promise。Promise 是 JavaScript 中用于处理异步操作的一种结构，它可以让你的代码更容易地组织和管理异步流程。

当你调用 `delay(ms)` 时，它会创建一个新的 Promise 对象，并立即执行 `setTimeout` 函数，该函数会在 `ms` 毫秒后触发回调函数。在这个回调函数里，`resolve` 被调用，表示异步任务完成并允许链式调用其他依赖这个延时操作的代码。

举个例子，如果你有这样一个代码片段：

const start = Date.now();
await delay(1000); // 等待1秒钟
const end = Date.now();

console.log('延迟后的时间:', end - start); // 输出1000毫秒

在这个场景中，`await delay(1000)` 表示主程序会暂停，直到1秒过后才继续执行接下来的任务。

相关问题

const sleep = (delay) => new Promise((r) => setTimeout(r, delay)) const tasks = { a: { job: async function () { await sleep(1000) console.log('Tasks A running') }, dependency: ['c', 'b'], }, b: { job: async function () { await sleep(3000) console.log('Tasks B running') }, dependency: [], }, c: { job: function () { console.log('Tasks C running') }, dependency: [], }, d: { job: function () { console.log('Tasks D running') }, dependency: ['c'], }, } function run(tasks) { // ...Write your answer here // The params `tasks` can be multiple of task, not just a、b、c、d. so don't answer with `a.job()` etc. // Answer should not include keyword of a/b/c/d } run(tasks) // desired outcome: // task B and task C get fired immediately // -> task D gets fired after task C finishes while task B is running in the background asyncrhously // -> once task B finishes, task A gets to run

Here's one possible implementation of the `run` function:

async function run(tasks) {
  const taskQueue = Object.entries(tasks)
    .filter(([_, task]) => task.dependency.length === 0)
    .map(([name, task]) => ({ name, task }))
  const runningTasks = {}

  while (taskQueue.length > 0) {
    const { name, task } = taskQueue.shift()
    const dependencies = task.dependency.map((depName) => runningTasks[depName])

    const isReady = dependencies.every((dep) => !!dep)
    if (!isReady) {
      taskQueue.push({ name, task })
      continue
    }

    console.log(`Running task ${name}`)
    const taskPromise = task.job()
    runningTasks[name] = taskPromise

    await taskPromise
    delete runningTasks[name]

    const dependents = Object.entries(tasks)
      .filter(([_, depTask]) => depTask.dependency.includes(name))
      .map(([depName, depTask]) => ({ name: depName, task: depTask }))
    taskQueue.push(...dependents)
  }
}

The `run` function uses a task queue to schedule and execute tasks in the correct order. It first adds all tasks with no dependencies to the queue. Then, in each iteration of the loop, it dequeues a task and checks if its dependencies have all finished running. If not, the task is pushed back to the end of the queue. If all dependencies are ready, the task is executed using its `job` function, and its promise is stored in the `runningTasks` object. Once the task finishes, its promise is removed from `runningTasks`, and any dependent tasks are added to the queue.

Note that this implementation assumes that all tasks have either a synchronous `job` function or an asynchronous one that returns a promise. If a task has an asynchronous `job` function that doesn't return a promise, it will need to be wrapped in a `Promise.resolve()` call.

Given a function fn, an array or arguments args, and a timeout t in milliseconds, return a cancel function cancelFn. After a delay of t, fn should be called with args passed as parameters unless cancelFn was called first. In that case, fn should never be called. Example 1: Input: fn = (x) => x * 5, args = [2], t = 20, cancelTime = 50 Output: [{"time": 20, "returned": 10}] Explanation: const cancel = cancellable(fn, [2], 20); // fn(2) called at t=20ms setTimeout(cancel, 50); the cancelTime (50ms) is after the delay time (20ms), so fn(2) should be called at t=20ms. The value returned from fn is 10.

Here's one possible implementation of the `cancellable` function in JavaScript:

function cancellable(fn, args, t) {
  let timerId;
  const promise = new Promise((resolve, reject) => {
    timerId = setTimeout(() => {
      resolve(fn(...args));
    }, t);
  });
  const cancelFn = () => {
    clearTimeout(timerId);
    promise.then(() => {
      console.log("Function call cancelled");
    });
  };
  return cancelFn;
}

The `cancellable` function takes three arguments: `fn`, the function to be called after a delay; `args`, an array of arguments to pass to `fn`; and `t`, the delay time in milliseconds.

The function returns a cancel function `cancelFn`, which can be called to cancel the delayed function call. If `cancelFn` is called before the delay time is up, `fn` will never be called and the promise returned from `cancellable` will be rejected.

In the example given, you would call `cancellable` like this:

const cancel = cancellable((x) => x * 5, [2], 20);

This sets up a delayed call to `fn`, which multiplies its argument by 5. The argument is 2, so the expected result is 10. The delay time is 20ms, and the cancel time is 50ms.

To cancel the delayed call, you would call `cancel()`:

setTimeout(cancel, 50);

This cancels the delayed call at the specified cancel time. Since the cancel time is after the delay time, `fn` will be called at t=20ms and will return the value 10.