我正在运行一个简单的程序进行长轮询，以检查数据库中是否发生任何更改，并将其发送到 Node.js 中的浏览器。我知道如何使用回调函数，但我需要从 program.query 函数返回一个值，因为我将在递归函数中使用它。感谢您的帮助。
var server=http.createServer(function(req,res){
program.run(res, 5);
});
server.on('listening',function(){
console.log('ok, server is running');
});
server.listen(9000);
var program = {
run: function(res, id, old){
if(old == undefined){
// I need a value from database to be returned to old variable
old = program.query(res, id /*, function(){res.end('there') }*/);
}
clearTimeout(tt);
var tt = setTimeout( function(){
// I need a value from database to be returned to new_ variable
var new_ = program.query(res, id /*, function(){res.end('there') }*/);
if(new_ != old){
// ... Send Response with the change to browser
}
else{ // no change in database, so run again
old = new_;
program.run(res, id, old);
}
}, 2000);
},
query: function(res, id /*,callback*/){
connection.query('SELECT table1.column1 FROM table1 WHERE table1.id ="'+id+'"', function(err, rows, fields){
//callback(res,id,rows[0].column1); // I don't want this solution
return rows[0].column1; // Not working..
});
}
};
最佳答案
只需在回调中递归调用即可。它看起来和听起来一样:
var program = {
run: function(res, id, old){
if(old == undefined){
program.query(res, id , function(res,id,result){
old = result;
clearTimeout(tt);
var tt = setTimeout( function(){
program.query(res, id , function(res,id,new_){
if(new_ != old){
// ... Send Response with the change to browser
}
else{ // no change in database, so run again
old = new_;
program.run(res, id, old);
}
// not sure where you want to put the res.end()
// since I don't really know your logic.
});
}, 2000);
});
}
else {
// This code is of course identical to the code above
// so you can refactor it out into its own function.
clearTimeout(tt);
var tt = setTimeout( function(){
program.query(res, id , function(res,id,new_){
if(new_ != old){
// ... Send Response with the change to browser
}
else{ // no change in database, so run again
old = new_;
program.run(res, id, old);
}
// not sure where you want to put the res.end()
// since I don't really know your logic.
});
}, 2000);
}
},
query: function(res, id, callback){
connection.query('SELECT table1.column1 FROM table1 WHERE table1.id ="'+id+'"', function(err, rows, fields){
callback(res,id,rows[0].column1);
});
}
};
关于mysql - 如何从 Node.js 中运行 Mysql Select 的函数返回值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/23621183/