使动态创建的承诺按顺序执行 [英] Make dynamically created promises execute in sequence

问题描述

如何动态创建一系列承诺并按顺序执行它们？

How can I dynamically create a series of promises and have them execute in sequence?

pseudocode
 for x=0 to maxValue
   promiseArray.push(createNewPromise(x))

 executeAllPromisesSequentially(promiseArray)

其中

executeAllPromisesSequentially is functionally equivalent to

promise1()
.then(promise2)
.then(promise3)
etc
...

推荐答案

我的要点

let tasks = [ /* ... */ ]
let promise = tasks.reduce((prev, task) => {
  return prev.then(() => {
    return task();
  });
}, Promise.resolve());
promise.then(() => {
//All tasks completed
});

顺序迭代模式

Sequential Iteration Pattern

let tasks = [ /* ... */ ]
let promise = Promise.resolve();
tasks.forEach(task => {
  promise = promise.then(() => {
    return task();
  });
});
promise.then(() => {
//All tasks completed
});

顺序迭代示例

Sequential Iteration Example

function spiderLinks(currentUrl, body, nesting) {
  let promise = Promise.resolve();
  if(nesting === 0) {
    return promise;
  }
  const links = utilities.getPageLinks(currentUrl, body);
  links.forEach(link => {
    promise = promise.then(() => spider(link, nesting - 1));
  });
  return promise;
}

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