小编ant*_*w3r的帖子

我要做的是将callback参数设置为一个函数可选.如果传递回调,则将值发送给回调函数,否则只返回该值.如果我省略回调,则返回undefined.

getByUsername = function(user_name, cb){
    async.waterfall([
        //Acquire SQL connection from pool
        function(callback){
            sql_pool.acquire(function(err, connection){
                callback(err, connection);
            });
        },
        //Verify credentials against database
        function(connection, callback){
            var sql = 'SELECT * FROM ?? WHERE ?? = ?';
            var inserts = ['users','user_name', user_name];
            sql = mysql.format(sql,inserts);
            connection.query(sql, function(err, results) {
                sql_pool.release(connection);
                callback(err, results);   
            });
        },
        //Create user object
        function(results, callback) {
            if(results.length < 1){
                if(cb){
                    cb(null);
                } else {
                    return null;
                }
            }else {
                var thisUser = new User(results[0]);
                if(cb){
                    cb(thisUser);
                } else …