Question

我想将值返回到varibales，所以我尝试使用return来编写它，但是确实没有工作

class move {
    getLastMove(id){


        var MoveRequest = "SELECT * FROM users ORDER BY id";

        var query = connection.query(MoveRequest, function(err,rows, result) {
        //console.log('rows', rows.length);
        if (rows.length == 0) { // evaluate the count
            return ("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
        }
        if (rows.length > 0) {
            for (var i in rows) {


                console.log('getLastMove',id);
                var move = rows[i].MoveString; 
                if (rows[i].GameId == id){

                    return move;
                }

            }
        }



        //console.log("Total Records:- " + result[0].total);

        });


            var move="rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
            return move;


    }


};

所以我试着像这样使用回调

class move {

        getLastMove(id){


            var MoveRequest = "SELECT * FROM users ORDER BY id";

            var query = connection.query(MoveRequest, function(err,rows, result,callback) {
            //console.log('rows', rows.length);
            if (rows.length == 0) { // evaluate the count
                callback ("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
            }
            if (rows.length > 0) {
                for (var i in rows) {


                    console.log('getLastMove',id);
                    var move = rows[i].MoveString; 
                    if (rows[i].GameId == id){

                        callback(move);
                    }

                }
            }



            //console.log("Total Records:- " + result[0].total);

            });


                var move="rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
                callback(move);


        }


    };

但是当运行回调示例时我得到此错误

TypeError：回调不是函数

Answer 1

    class move {

        getLastMove(id,callback){
            var query = connection.query(MoveRequest, function(err,rows, result) {
                //do some operation then
                 if (rows.length > 0) {
                    for (var i in rows) {
                        console.log('getLastMove',id);
                        var move = rows[i].MoveString; 
                        if (rows[i].GameId == id){
                            callback(err,move) //<-------
                        }
                   }
                }

           });
        }                
    };

var moveInstance = new move();

moveInstance.getLastMove(id,function(err,result){ //code here })

Answer 2

你以错误的方式使用回调。将回调传递给getLastMove（）：

class move {
getLastMove(id, callback){
    var MoveRequest = "SELECT * FROM users ORDER BY id";

    var query = connection.query(MoveRequest, function(err,rows, result) {
        if(err) {
            return callback(err)
        }

        if (rows.length == 0) { // evaluate the count
            return callback (null, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
        }
        if (rows.length > 0) {
            for (var i in rows) {
                if (rows[i].GameId == id){
                    callback(null, rows[i].MoveString);
                }
            }
        }
    });
}

};

假设moveObj是move类型的对象，请调用函数getLastMove，如：

var moveObj = new move();
moveObj.getLastMove(34, function (err, data) { // 34 is the value of `id`
    if(err) {
        // There was some error in execution of getLastMove; var `err` has info regarading that. 
        return console.log("There was some err while executing getLastMove", err);
    }

    // If no Error, process your `data` accordingly
    console.log("Data returned by callback", data);
});

node.js使用类函数的回调

2 个答案: