Hello I am new to promises and callbacks in node js I am doing something to fetch users list using another function using callbacks but getting fail. somewhere I found to use promises. but never used promises. can anyone help me with code?
send_noti('12', function(res){
console.log(res);
});
function send_noti(value, callback){
connection.query(" SELECT * from users ", function( err, res ){
callback( res );
});
}
You're looking for something like this:
function sendNotiAsync(value) {
return new Promise((resolve, reject) => // Promise constructor
connection.query("SELECT * from users", (err, data) => // Perform the action
err ? reject(err) : resolve(data))); // If error exists, reject, else resolve
}
And use it like this:
sendNotiAsync(someValue)
.then(data => {
// Work with data here, for example
console.log(data);
})
.catch(err => {
// Handle errors here
console.error(err);
});
In node callbacks of async functions should always have the signature function(err, result /*,...*/)
Your example should look like:
send_noti('12', function(err, res) {
if( !err ) {
console.log(res);
}
});
function send_noti(value, callback) {
connection.query(" SELECT * from users ", callback );
}
Beside that your example does not use Promises. With Promises it would look like this:
send_noti('12')
.then(function(res) {
console.dir(res)
})
.catch(function(err) {
console.dir(err)
})
function send_noti(value, callback) {
return new Promise(function(resolve, reject) {
try {
connection.query(" SELECT * from users ", function(err, res) {
if (err) {
reject(err);
} else {
resolve(res);
}
});
} catch (err) {
reject(err);
}
})
}