I am new to nodejs. Here, I want to avoid callback using Co generators with promises. But when I execute this code, it only executes first yield or does not assign the result of get function to processedData0 variable. How to solve this ?
co(function *() {
console.log("hello");
try{
console.log("hello");
var processedData0= yield Promise.promisify(get);
//console.log("hello");
var processedData1 = yield Promise.promisify(abc1)(processedData0);
//console.log("hello2");
var processedData2 = yield Promise.promisify(xyz)(processedData1);
//console.log("hello3");
var processedData3 = yield Promise.promisify(pqr)(processedData2);
// console.log("success");
} catch (err) {
throw err;
}
})
This is my get function :-
function get(err,rows){
connection.connect(function(err){
if (err)
{
console.error('error connecting: ' + err.stack);
return;
}
else{
console.log("connected to database");
connection.query("SELECT count(id) as count from abc where name=? AND email=?",[username,password],function(err,rows){
if(err){throw err}
else{
b=rows;
return rows;
console.log(b);
}
});
}
});
}
This is my abc1 function:-
function abc1(err,rows){
console.log("onresult");
if(err)
{
throw err;
console.log("error in Query");
}
else
{
if(rows[0].count!=1)
{
//xyz(result,xyz);
res.json({
"status": 401,
"message": "Invalid credentials"
});
}
else
{ connection.query("SELECT email from abc where name=? AND email=?",[username,password],function(err,rows){} );
//res.json(genToken("ayush"));
}
}
}
This is my xyz function:
function xyz(err,rows){
if(err)
{
console.log(err);
}
console.log(rows);
connection.query("SELECT name from abc where name=? AND email=?",[username,password],function(err,rows){} );
}
This is my pqr function:
function pqr(err,rows){
if(err)
{
console.log(err);
}
console.log(rows);
}
来源：https://stackoverflow.com/questions/30860857/avoiding-callback-hell-using-generators-and-promises-co-module