我建议看一看MDN的Promise文档，它为使用Promises提供了一个很好的起点。或者，我肯定网上有很多教程。:）

注意:现代浏览器已经支持ECMAScript 6 specification of Promises（请参阅上面链接的MDN文档），我假设您希望使用本机实现，而不需要第三方库。

作为一个实际的例子。。。

基本原理是这样工作的:

1. 您的API称为
2. 创建一个新的Promise对象，该对象将一个函数作为构造函数参数
3. 您提供的函数由基础实现调用，并且该函数被赋予两个函数-resolve和reject
4. 完成逻辑操作后，调用其中一个来实现承诺或以错误拒绝承诺

这看起来可能很多，所以这里有一个实际的例子。

exports.getUsers = function getUsers () {
  // Return the Promise right away, unless you really need to
  // do something before you create a new Promise, but usually
  // this can go into the function below
  return new Promise((resolve, reject) => {
    // reject and resolve are functions provided by the Promise
    // implementation. Call only one of them.

    // Do your logic here - you can do WTF you want.:)
    connection.query('SELECT * FROM Users', (err, result) => {
      // PS. Fail fast! Handle errors first, then move to the
      // important stuff (that's a good practice at least)
      if (err) {
        // Reject the Promise with an error
        return reject(err)
      }

      // Resolve (or fulfill) the promise with data
      return resolve(result)
    })
  })
}

// Usage:
exports.getUsers()  // Returns a Promise!
  .then(users => {
    // Do stuff with users
  })
  .catch(err => {
    // handle errors
  })

在Node.js7.6中，升级了v8 JavaScript编译器，支持Async/Await。现在可以将函数声明为async，这意味着它们自动返回promise，当异步函数完成执行时，该函数将被解析。在此函数内部，可以使用await关键字等待另一个承诺解决。

下面是一个例子:

exports.getUsers = async function getUsers() {
  // We are in an async function - this will return Promise
  // no matter what.

  // We can interact with other functions which return a
  // Promise very easily:
  const result = await connection.query('select * from users')

  // Interacting with callback-based APIs is a bit more
  // complicated but still very easy:
  const result2 = await new Promise((resolve, reject) => {
    connection.query('select * from users', (err, res) => {
      return void err ? reject(err) : resolve(res)
    })
  })
  // Returning a value will cause the promise to be resolved
  // with that value
  return result
}

使用bluebird，您可以使用Promise.PromisifyAll（和Promise.Promisify)向任何对象添加Promise ready方法。

var Promise = require('bluebird');
// Somewhere around here, the following line is called
Promise.promisifyAll(connection);

exports.getUsersAsync = function () {
    return connection.connectAsync()
        .then(function () {
            return connection.queryAsync('SELECT * FROM Users')
        });
};

并像这样使用:

getUsersAsync().then(console.log);

或

// Spread because MySQL queries actually return two resulting arguments, 
// which Bluebird resolves as an array.
getUsersAsync().spread(function(rows, fields) {
    // Do whatever you want with either rows or fields.
});

Bluebird支持许多功能，其中之一是处理程序，它允许您在连接结束后，在promise.using和promise.prototype.disposer的帮助下安全地处理连接。下面是我的应用程序中的一个例子:

function getConnection(host, user, password, port) {
    // connection was already promisified at this point

    // The object literal syntax is ES6, it's the equivalent of
    // {host: host, user: user, ... }
    var connection = mysql.createConnection({host, user, password, port});
    return connection.connectAsync()
        // connect callback doesn't have arguments. return connection.
        .return(connection) 
        .disposer(function(connection, promise) { //Disposer is used when Promise.using is finished. connection.end(); });
}

那就这样用吧:

null

exports.getUsersAsync = function () {
    return Promise.using(getConnection()).then(function (connection) {
            return connection.queryAsync('SELECT * FROM Users')
        });
};

null

一旦承诺用值解析（或用错误拒绝），这将自动结束连接。

Node.js版本8.0.0+:

您不必再使用bluebird来承诺节点API方法。因为，从版本8+开始，您可以使用本机util.promisify:

const util = require('util');

const connectAsync = util.promisify(connection.connectAsync);
const queryAsync = util.promisify(connection.queryAsync);

exports.getUsersAsync = function () {
    return connectAsync()
        .then(function () {
            return queryAsync('SELECT * FROM Users')
        });
};

现在，不需要使用任何第三方自由来做承诺。