This question already has an answer here:
-
How do I convert an existing callback API to promises?
17 answers
I have an ajax call which needs to return a promise. The function is as follows
client.tickets.create(ticket, function(err, req, result) {
if (err) {
logger.error(err);
return false;
}
return JSON.stringify(result);
});
I have to wait for this function to execute before I can perform the next action. How can I promisify this function ?
I tried the following and it gave me an error saying Cannot call method then of undefined
:
return client.tickets.create(ticket).then(function(result){
return JSON.stringify(result);
},function(err){
logger.error(err);
return false;
});
You have the error because create()
is not a Promise. Promisifying an async function is quite easy (nodejs has a built-in Promise support nowadays):
function createTicket(ticket) {
// 1 - Create a new Promise
return new Promise(function (resolve, reject) {
// 2 - Copy-paste your code inside this function
client.tickets.create(ticket, function (err, req, result) {
// 3 - in your async function's callback
// replace return by reject (for the errors) and resolve (for the results)
if (err) {
reject(err);
} else {
resolve(JSON.stringify(result));
}
});
});
}
// 4 - consume your promise with then() (resolved promise) and catch (rejected promise)
createTicket(ticket).then(function (result) {
// deal with result here
}).catch(function (err) {
// deal with error here
});
rather than manually wrapping async code into promises, I would advice using libraries like Bluebird
to do that for you:
var Bluebird = require('bluebird');
//either
client.tickets = Bluebird.promisifyAll(client.tickets);
//or
client.tickets.createAsync = Bluebird.promisify(client.tickets.create);
...
return client.tickets.createAsync(ticket)
.then(JSON.stringify)
.catch(err => {
logger.error(error);
return false
});
function createTicket(){
var deferred = Q.defer()
client.tickets.create(ticket, function(err, req, result) {
if (err) {
logger.error(err);
return deferred.reject(err)
}
return deferred.resolve(result)
});
}
createTicket().then(function(){
//success here
}, function(){
//failure here
});
Using Q api you can achive promise.