javascript - 我们如何在 Node.js 中使用 Promise？

Question

就像在异步编程中一样，我们习惯于回调和 promise 。 这里我陷入了一个可能习惯于promise的问题。我用谷歌搜索了很多，但没有发现任何东西可以解决我的问题。

这是我正在执行的在 Android 设备中发送推送通知的代码。

router.post('/check-notifications', function(req, res, next) {

    var user_id = req.body.user_id;

    var response = {};
    var gcm = require('push-notify').gcm({

        apiKey: gcm_apiKey,
        retries: 0
    });

    connection.query('select device_id from devices where user_id = '+ user_id, function (err, result) {
        if ( result.length ) {

            for (var i = 0; i < result.length; i++) {

                console.log(i + 'before notify');
                gcm.send({

                    registrationId: result[i]['device_id'],
                    data: result[0]
                });

                console.log(i + 'before transmitted');
                gcm.on('transmitted', function (result, message, registrationId) {
                    console.log('transmitted');
                });

                gcm.on('transmissionError', function (error, message, registrationId) {
                    console.log(message);
                });

                console.log(i + 'after notify');

            }
        }           
    });

    response['success'] = true;
    response['msg'] = 'sent successfully';
    res.json(response);
}); 

输出:

0before notify
0before transmitted
0after notify
1before notify
1before transmitted
1after notify
transmitted
transmitted
transmitted
transmitted

我认为应该是这样的。

0before notify
0before transmitted
transmitted
0after notify
1before notify
1before transmitted
transmitted
1after notify

Answer 1

您可以使用async.mapSeries链接通知的方法。将 for 循环替换为:

async.mapSeries(result, function(item, callback) {
    gcm.send({
        registrationId: item['device_id'],
        data: data
    });
    gcm.on('transmitted', function(result, message, registrationId) {
        console.log('transmitted');
        callback(null, message, registrationId);
    });

    gcm.on('transmissionError', function(error, message, registrationId) {
        callback(error, message, registrationId);
    });
}, function (err, results) {
    if (err) throw err;
    response['success'] = true;
    response['msg'] = 'sent successfully';
    res.json(response);
})