如何动态地向promises链添加新的承诺

Question

我想创建promises链，然后根据需要动态添加尽可能多的promises。 这些添加可能在一些循环中具有动态步数，因此我不能使用链接，如.then（）。then（）。然后...代码bellow工作不正常，但你会得到这个想法。 结果应该是一个控制台在3,4和5秒内记录了3000,4000,5000个数字，但实际上并不是这样。 有任何想法吗？

let launchChain = function(delay)
{
  return new Promise((resolve: Function, reject: Function) => {
    setTimeout(() => {
      console.log(delay);
      resolve();
    }, delay)
  })
}

let chain = launchChain(3000);

chain.then(function () {
  return launchChain(4000);
})

chain.then(function () {
  return launchChain(5000);
})

Answer 1

function run(delay){
    let chain = launchChain(delay);
    chain.then(function() {
        run(delay+1000);
    });
}


run(3000);

Answer 2

所以使用reduce和这个网站

 var delays = [0, 1000, 2000, 3000, 4000]; function workMyCollection(arr) { return arr.reduce(function(promise, item) { return promise.then(function() { return launchChain(item); }); // uses this orignal promise to start the chaining. }, Promise.resolve()); } function launchChain(delay) { return new Promise(function(resolve, reject) { setTimeout(function() { console.log(delay); resolve(); }, delay); }); } workMyCollection(delays); 

[编辑]：另一种方式

 var delays = [0, 1000, 2000, 3000, 4000]; var currentPromise = Promise.resolve(); for (let i = 0; i < delays.length; i++) { // let makes i block scope .. var would not have done that currentPromise = currentPromise.then(function() { return launchChain(delays[i]); }); } function launchChain(delay) { return new Promise(function(resolve, reject) { setTimeout(function() { console.log(delay); resolve(); }, delay); }); } 

如果这对你有用，请告诉我:)由于这个问题，我学到了很多东西！

Answer 3

谢谢sinhavartika！ 有用！ 但我实际上从这里举了个例子https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce并稍微改了一下，现在我在下面的项目中使用它方式：

  /**
   * Runs promises from promise array in chained manner
   *
   * @param {array} arr - promise arr
   * @return {Object} promise object
   */
  function runPromiseInSequense(arr) {
    return arr.reduce((promiseChain, currentPromise) => {
      return promiseChain.then((chainedResult) => {
        return currentPromise(chainedResult)
          .then((res) => res)
      })
    }, Promise.resolve());
  }

  var promiseArr = [];

  function addToChain(delay)
  {
    promiseArr.push(function (delay) {
      return new Promise((resolve, reject) => {
          setTimeout(() => {
            console.log(delay);
            resolve();
          }, delay)
      });
    }.bind(this, delay))
  }

  addToChain(1000);
  addToChain(2000);
  addToChain(3000);
  addToChain(4000);

  runPromiseInSequense(promiseArr);