javascript - Node JS 回调

Question

在理解回调时遇到一些困难，这是我的身份验证代码(通过 MySQL)

function authenticate(username, password, callback) {
    var query = "SELECT * from mydb.users where username='" + username + "'and BINARY password='" + password + "'";
    connection.query(query, function (err, rows) {
        if (rows[0] != undefined) {
            if ('username' in rows[0]) {
                if (rows[0].username == username) {
                    callback(true);
                }
            }
        }
        callback(false);
    });
};

exports.assets=function(req,res) {
    var username = req.param("username");
    var password = req.param("password");

    authenticate(username, password, function (didAuthenticate) {
        if (didAuthenticate) {
            console.log("Authenticated");
        }
        else {
            console.log("Failed");
        }
    }); 
};

用户/密码匹配时输出:

Authenticated
Failed

没有匹配:

Failed

为什么当 didAuthenticate 返回 true 时 if/else 语句不起作用？

Answer 1

简单地执行callback(...)并不会结束函数的执行；您需要一个 return 语句来告诉函数停止运行，如下所示:

function authenticate(username, password, callback) {
    var query = "SELECT * from mydb.users where username='" + username + "'and BINARY password='" + password + "'";
    connection.query(query, function (err, rows) {
        if (rows[0] != undefined) {
            if ('username' in rows[0]) {
                if (rows[0].username == username) {
                    return callback(true);
                }
            }
        }
        return callback(false);
    });
};

当您阅读其他 NodeJS 代码时，您将看到使用此技术。