javascript - 如果回调存在则执行 Callback(obj) 否则返回对象

Question

我想做的是使函数的回调参数可选。如果传递了回调，则将值发送给回调函数，否则只需返回值。如果我省略回调，我将返回 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 {
                    return thisUser;
                }
            }
        }], function (err, results) {
            throw new Error('errrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrroooooorrrrrrrr');
        }
    )
}

Answer 1

你可以这样检查:

if(cb && typeof cb === "function") {
    cb(num + 1);
}

注意:确保您实际使用的是 cb 来调用您的回调函数，而不是 callback ;)