如何将回调地狱重写为承诺？答案

【问题标题】：how to rewrite callback hell into promise?如何将回调地狱重写为承诺？
【发布时间】：2018-01-24 16:43:35
【问题描述】：

我的回调地狱路线运行良好...

var myCallbackHell = router.route('/');
myCallbackHell.get(function(req, res, next) {
  bookModel.find({title: "Animal Farm"}).then(function(book) {
    movieModel.find({title: "Intouchables"}).then(function(movie) {
      gameModel.find({title: "The Last of Us"}).then(function(game) {
        res.render('index', {book_found: book, movie_found: movie, game_found: game});
      });
    });
  });
});

但是我想使用 Promise。任何帮助，提示？

【问题讨论】：

不仅仅是回调地狱，您的代码看起来更像是一个承诺地狱。

标签： javascript callback promise

【解决方案1】：

你可以用Promise.all写同样的，像这样

var promises = [
  bookModel.find({title: "Animal Farm"}),
  movieModel.find({title: "Intouchables"}),
  gameModel.find({title: "The Last of Us"})
];

Promise.all(promises).then(function(values) {
  res.render('index', {book_found: values[0], movie_found: values[1], game_found: values[2]});
}).catch(function(err) {
  // deal with err
});

【讨论】：

【解决方案2】：

ES2017 有 async/await 语法

为了防止Promise地狱

var myCallbackHell = router.route('/');
myCallbackHell.get( async function(req, res, next) {
    var book = await bookModel.find({title: "Animal Farm"})
    var movie = await movieModel.find({title: "Intouchables"})
    var game = await gameModel.find({title: "The Last of Us"})

    res.render('index', {book_found: book, movie_found: movie, game_found: game});
})

您应该捕获错误并拒绝，因此：

router.get('/', async function(req, res, next) {
    try {
        var book = await bookModel.find({title: "Animal Farm"})
        var movie = await movieModel.find({title: "Intouchables"})
        var game = await gameModel.find({title: "The Last of Us"})

        res.render('index', {book_found: book, movie_found: movie, game_found: game}) 

    } catch (e) { next(e) }
})

【讨论】：