我如何同步这 3 个基于 promise 的函数？

Question

如何同步这 3 个 promise 返回函数（例如在其他函数中）？我想获得以下输出 -> 开始 -> (2secs)..2..(3secs)..3..(4secs)..4 -> 结束。我试过生成器，但我的输出不是那样的（可能我做错了什么）

function resolveAfter2Seconds() {
  new Promise(resolve => {
    setTimeout(() => {
      resolve('resolved 2');
      console.log('2')
    }, 2000);
  });
}
function resolveAfter3Seconds() {
  new Promise(resolve => {
    setTimeout(() => {
      resolve('resolved 2');
      console.log('3')
    }, 3000);
  });
}
function resolveAfter4Seconds() {
 new Promise(resolve => {
    setTimeout(() => {
      resolve('resolved 2');
      console.log('4')
    }, 4000);
  });
}

Answer 1

首先，将函数更改为 return 他们的承诺。例如：

function resolveAfter2Seconds() {
  return new Promise(resolve => { // <------ added return statement
    setTimeout(() => {
      resolve('resolved 2');
      console.log('2')
    }, 2000);
  });
}

然后将承诺链接在一起[=13=]

resolveAfter2Seconds()
  .then(() => resolveAfter3Seconds())
  .then(() => resolveAfter4Seconds());

或使用async/await语法：

async function exampleFunction() {
  await resolveAfter2Seconds();
  await resolveAfter3Seconds();
  await resolveAfter4Seconds();
}

Answer 2

您可能想尝试链接以获得顺序输出：

resolveAfter2Seconds()
  .then(() => resolveAfter3Seconds())
  .then(() => resolveAfter4Seconds())

PS。不要忘记对这些功能做出 return 承诺。

我如何同步这 3 个基于 promise 的函数？

How can i synchronize these 3 promise-based functions?

javascript

async-await

es6-promise