javascript - 使用 bluebird 从 JSON 构建 Promise

Question

我有一个 uniq 问题。我有 JSON 数据，它表示生成 promise 的步骤。

[
  {
     action: 'wait' 
  },
  {
     action: 'screenshot' 
  }
]

现在我正在与 Bluebird 做出这个 promise 。

var pr = require('bluebird/js/main/promise')();
var R = require('bluebird');

var Worker = {
  open: function () {
    return new pr(function (resolve, reject) {
      resolve('opened');
    });
  },
  wait: function (milliseconds) {
    return pr.delay(milliseconds);
  },

  screenshot: function (milliseconds) {
    return new pr(function (resolve, reject) {
      resolve('take screenshot');
    });
  }
}

var defers = [];
Worker.open();
JSON.forEach(function (vl) {
  var defer = R.defer();
  defers.push(defer.promise);
  Worker[vl.action]().then(function () {
    // do something
    defer.resolve();
  });
});
R.all(defers).then(function () { console.log('finished');});

现在这不起作用，因为 promise 没有被链接。有人建议我把它们拴起来。

 var pr = require('bluebird/js/main/promise')();
var R = require('bluebird');

var Worker = {
  open: function () {
    return new pr(function (resolve, reject) {
      resolve('opened');
    });
  },
  wait: function (milliseconds) {
    return pr.delay(milliseconds);
  },

  screenshot: function (milliseconds) {
    return new pr(function (resolve, reject) {
      resolve('take screenshot');
    });
  }
}

var defers = [];
var chain = Worker.open();
JSON.forEach(function (vl) {
  var defer = R.defer();
  defers.push(defer.promise);
  chain = chain[vl.action]().then(function () {
    // do something
    defer.resolve();
  });
});
R.all(defers).then(function () { console.log('finished')});

但这也不起作用，关于如何从 JSON 数据生成基于 Promise 的函数有什么建议吗？

Answer 1

您想要采取一系列操作，并将其减少为单个 Promise 值。

const actions = [
  {action: 'wait'},
  {action: 'screenshot'}
];

const allDone = actions.reduce((promise, item) => 
  promise.then(Worker[item.action]), Promise.resolve());

allDone.then(() => console.log("All done!"));

这读作:“通过从空 Promise 开始，使用 .then() 将项目的操作链接到 Promise 来减少数组。”

<小时/>

根据请求，使用 ES5(学习 ES2015，太棒了!)

var actions = [
  {action: 'wait'},
  {action: 'screenshot'}
];

var allDone = actions.reduce(function(promise, item) {
  return promise.then(Worker[item.action])
}, Promise.resolve());

allDone.then(function() { 
  console.log("All done!"); 
});