JavaScript Promise 封装在函数中还是裸露的？

Question

如果我调用一个 Promise 函数，我是否需要执行“将其包装在另一个函数中”层？

Promise
.resolve()
.then(()=>{ // this part seems excessive
  return new Promise(resolve={
  // my function's guts

我可以直接返回新的 Promise，例如

Promise
.resolve()
.then(new Promise(resolve={
  // my function's guts

Answer 1

If I'm calling a function that is a promise, do I need to do this "wrap it in another function" layer?

是的，否则它将立即执行，我建议您在命名函数中创建您的 promise ，这样您就可以保持链整洁和可读，并且代码更可重用。

myTask1()
  .then(myTask2)
  .then(myTask3);

function myTask1() {
  return new Promise((resolve, reject) => {
    console.log("Task 1");
    resolve("Task 1");
  })
}

function myTask2() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log("Task 2");
      resolve("Task 2");
    }, 1000)

  })
}

function myTask3() {
  return new Promise((resolve, reject) => {
    console.log("Task 3");
    resolve("Task 3");
  })
}

Can I return the new promise directly, like.... .then(new Promise(resolve={?

不，像这样实例化 promise 有一个关键的区别。当您将 Promise 包装在函数中时，直到前一个 Promise 完成后才会对其进行求值，而如果您内联实例化它，则会立即对其进行求值，这可能会导致意外结果:

new Promise((resolve, reject) => {
    resolve()
  })
  .then(new Promise((resolve, reject) => {
    console.log("Task 1");
  }))
  .then(new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log("Task 2");
      resolve("Task 2");
    }, 1000);
  }))
  .then(new Promise((resolve, reject) => {
    console.log("Task 3");
    resolve("Task 3");
  }))

要使上述工作正常进行，您可以对其进行更改，以便闭包返回一个 promise ，但它开始看起来非常困惑:

new Promise((resolve, reject) => {
    resolve()
  })
  .then(() => {
    return new Promise((resolve, reject) => {
      console.log("Task 1");
      resolve("Task 1");
    })
  })
  .then(() => {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        console.log("Task 2");
        resolve("Task 2");
      }, 1000);
    });

  })
  .then(() => {
    return new Promise((resolve, reject) => {
      console.log("Task 3");
      resolve("Task 3");
    });
  })