javascript 如果回调存在则执行回调（obj）否则返回对象
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Execute Callback(obj) if callback Exists Else return object
提问by ant_iw3r
What I'm trying to do is make the callback parameter to a function optional. If a callback is passed send the value to the callback function else simply return the value. If I omit the callback I get undefined returned.
我想要做的是使回调参数成为可选的函数。如果传递了回调，则将值发送到回调函数，否则只需返回该值。如果我省略回调，我会返回 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');
}
)
}
回答by Floremin
You could just check like this:
你可以这样检查：
if(cb && typeof cb === "function") {
cb(num + 1);
}
NOTE: Make sure you're actually using cbto call your callback function and not callback;)
注意：确保您实际上是cb用来调用回调函数而不是callback;)
