Callback VS Event

callback-vs-event

/**
 * 显示指定用户 profile 页面
 * 
 * 获取关注和被关注的数据
 * 获取此用户最近的活动数据
 *  - 活动数据里面包含各种数据的聚合
 * 判断当前登录的用户与指定用户是否已经相互关注
 * 
 */

// callback 
exports._show = function(req, res, next) {
    var current_user_id = req.session.user_id;
    var query = {user_id: req.user.id};
    if(req.query.max) {
        query.create_at = {$lt: new Date(req.query.max)};
    }
    var relation_reader = read_relaction(req.user.id, current_user_id);
    var follow_counts_reader = read_follower_and_following_counts(req.user.id);
    get_logs(query, function(err, logs) {
        if(err) return next(err);
        relation_reader(function(err, relation) {
            if(err) return next(err);
            if(relation && relation.length > 0) {
                req.user.focus = true;
            }
            follow_counts_reader(function(err, follower_count, following_count) {
                if(err) return next(err);
                req.user.follower_count = follower_count;
                req.user.following_count = following_count;
                
                if(req.xhr) {
                    res.partial('log', logs);
                } else {
                    res.render('user/detail', {user: req.user, logs: logs});
                }
            });
        });
    });
};

// change to EventEmitter
exports.show = function(req, res, next) {
    var current_user_id = req.session.user_id
      , query = {user_id: req.user.id};
    if(req.query.max) {
        query.create_at = {$lt: new Date(req.query.max)};
    }
    var event = new EventEmitter(), locals = {}, step_count = 3;
    if(req.xhr) {
        step_count = 1;
    }
    event.on('step_done', function() {
        if(--step_count == 0) {
            event.emit('finished');
        }
    });
    event.on('finished', function() {
        if(req.xhr) {
            res.partial('log', locals.logs);
        } else {
            if(!locals.user) {
                locals.user = req.user;
            }
            res.render('user/detail', locals);
        }
    });
    event.on('error', function(err) {
        event.removeAllListeners();
        next(err);
    });
    
    if(!req.xhr) {
        if(current_user_id) {
            Relation.findOne({uid: req.user.id, fid: current_user_id}, function(err, relation) {
                if(err) {
                    event.emit('error', err);
                } else {
                    if(relation) {
                        req.user.focus = true;
                    }
                    event.emit('step_done');
                }
            });
        } else {
            event.emit('step_done', 'relation', null);
        }
        
        read_follower_and_following_counts(req.user.id)(function(err, follower_count, following_count) {
            if(err) {
                return event.emit('error', err);
            }
            req.user.follower_count = follower_count;
            req.user.following_count = following_count;
            event.emit('step_done');
        });
    }
    
    get_logs(query, function(err, logs) {
        if(err) {
            return event.emit('error', err);
        }
        locals.logs = logs;
        event.emit('step_done');
    });
};