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/ 8 Years ago, wed, september 28, 2016, 12:00:00
I am trying to understand promises in node.js. Here is a sample code
con.queryReturnPromise(SELECT * FROM bookings WHERE driverId = + accId + AND bookingStatus = + config.get('BOOKING_STATUS_ACTIVE') + LIMIT 1)
.catch((err) => {
callback({
message: Success,
error: true,
});
console.log(mysql query error);
return Promise.reject();
})
.spread((rows, fields) => {
if (rows.length != 1) {
return Promise.reject();
}
mBooking = rows[0];
var query = INSERT INTO locations SET timeStamp = + timeStamp + latitude = + lat + , longitude = + lng + , bookingId = + mBooking.id;
return con.queryReturnPromise(query)
})
.catch((err) => {
if (err)
console.log(Adding Location error + err);
return Promise.reject();
})
.spread(() => {
return funcs.getBooking(con, mBooking.id)
})
.then((booking) => {
if (mBooking.userId.toString() in userSockets) {
userSockets[mBooking.userId].emit(config.get('EVENT_USER_UPDATE_BOOKING'), {
message: Success,
error: false,
booking: booking
});
userId = mBooking.userId.toString();
}
callback({
message: Success,
error: false,
booking: booking
});
})
.catch((err) => {
if (err)
console.log(err);
});
The code is quite simple. However i have one confusion. If return Promise.reject() is being called, where would the function lead to, Which code will be called. E.g if the first catch clause is called and it calls return Promise.reject() where part of below code will run afterwards
Promises in for loop
data = JSON.parse(data);
var promisesArray = [];
for (var i = 0; i < data.length; i++)
{
var location = data[i];
var lng = location.lng;
var lat = location.lat;
var bearing = location.bearing;
var deltaTime = location.deltaTime;
var timeStamp = location.timeStamp;
var query = INSERT INTO locations SET timeStamp = + timeStamp + latitude = + lat + , longitude = + lng + , bookingId = + mBooking.id;
var promise = con.queryReturnPromise(query)
.then( () => {
});
promisesArray[] = promise;
}
Promise.all(promisesArray)
.then(function(results)
{
callback({
error: false,
});
});
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