We Keep Coding

sync function that await an event (once more

Desperately trying to write a sync version of https://www.npmjs.com/package/node-firebird#reading-blobs-aasynchronous
Basically I need to (a)wait twice:
for the callback function to execute so that the eventEmitter is available
for the "end" event to occur
and then return the Buffer.
my code (JS/TS mix for now) currently does 2, but not 1 : readBlob returns undefined, then Buffer.concat(buffers) is called later ... :
function readBLOB(callback: any): Buffer {
return callback(async (err, _, eventEmitter) => {
let buffers = []
if (err)
throw err
eventEmitter.on('data', chunk => {
buffers.push(chunk);
});
return await eventEmitter.once('end', function (e) {
return Buffer.concat(buffers)
})
})
}
Sorry to ask one more time (yes, I checked a lot of other questions and tried a lot of things...), but how to make this work (simply...) ?
(the function that calls the callback is fetch_blob_async in https://github.com/hgourvest/node-firebird/blob/master/lib/index.js#L4261 , just in case...)

There are few mistakes here like returning an callback function, witch returns, i guess, undefined or returning something IN an callback function that makes no sense.
Also async / await makes no sense here it has no effect. async / await is only useful if you want to await till some Promise resolves. But you have no Promise in your code at all.
What you need is new Promise
function readBLOB(callback) {
return new Promise((resolve, reject) => {
callback((err, _, eventEmitter) => {
let buffers = [];
if (err) reject(err);
eventEmitter.on("data", chunk => {
buffers.push(chunk);
});
eventEmitter.once("end", function(e) {
resolve(Buffer.concat(buffers));
});
});
});
}
Simple like that. You resolve your Buffer and reject if some error occurs
Now you can use it like:
readBLOB(cb).then(data => {
console.log(data);
})

How to correctly string together Promises for synchronous code execution

I posted a similar question several days ago but I have made some changes and commenting on that question was becoming tedious, so it was recommended I ask a new question.
The idea is that I want to execute four equations synchronously. Inside those equations are HTTP requests. I have two of the equations working properly and but there is one equation that involves two POST requests and a GET requests. The second requests relies on the first and the third request relies on the second.
I have tried several different methods to get this to work. I have tried flattening my promises, returning the promises. All kinds of things, with no luck. I am not sure where I am going wrong.
Synchronous code snippet:
this.getData1(user, userID).then(() =>
{
this.getData2(user, userID)
.then(() =>
{
this.getData3(user, lan).then(() =>
{
this.userCheck(user);
})
});
});
I have getData2 and getData3 working.
getData1 looks like:
getData1(user: string, id: string){
console.log('grabbing CC information', id, user);
return new Promise((resolve, reject) =>
{
var status: string;
this._apiService.getAssertion(id).subscribe((data: any) =>
{
let assert = data.toString();
this._apiService.getToken(assert).subscribe((data: any) =>
{
let tkn = data.access_token.toString();
this._apiService.ccMeta(tkn, guid).subscribe((data: any) =>
{
parseString(data, (err, result) =>
{
if (err)
{
throw new Error(err);
}
else
{
status = result['entry']['content'][0]['m:properties'][0]['d:status'][0];
this.ccData.push(
{
key: 'userStatus',
value: status
})
}
});
});
});
});
resolve()
});
}
I also tried something like this previously. It did not work either.
apiService.getAssertion(id).then(assert =>
{
return apiService.getToken(assert.toString(), user);
}).then(data =>
{
return apiService.ccMeta(data.access_token.toString(), id);
}).then(parseStringPromise).then(information =>
{
this.ccData.push(
{
key: 'userStatus',
value: information.entry
});
});
Inside this function the getAssertion function is a POST request. The getToken function is another POST request that relies on the assertion from the first POST request. Finally, ccMeta is a get request that relies on the token from the second POST request.
I would expect getData1 to execute first, then getData2, then getData3, and finally, userCheck. Inside getData1 I need the assertion, then the token, and then get request to execute synchronously. The code snippet above is not executing correctly. The assertion is not properly being used in the getToken equation.
I would greatly appreciate some help.

Since these HTTP calls are in fact observables and not promises, I think you should look into observable composition using pipe and switchMap for instance. If you still want you method to return a promise, it could look like this:
getData1(user: string, id: string) {
console.log('grabbing CC information', id, user);
return new Promise((resolve, reject) => {
this._apiService.getAssertion(id)
.pipe(
switchMap((data: any) => {
let assert = data.toString();
return this._apiService.getToken(assert);
}),
switchMap((data: any) => {
let tkn = data.access_token.toString();
return this._apiService.ccMeta(tkn, guid);
}),
)
.subscribe(
data => {
parseString(data, (err, result) => {
if (err) {
reject(new Error(err));
return;
}
const status: string = result['entry']['content'][0]['m:properties'][0]['d:status'][0];
this.ccData.push({
key: 'userStatus',
value: status
});
resolve();
});
},
);
});
}

Can you add a .then to a promise after it's created?

Promises just baffle me.
I'm trying to make a mock data service to imitate axios.
My mock put call passes a targetUrl to _fetch which then sees if it's a valid url and either returns a new Promise with a delayed .resolve
const _returnResponse = (mockData, time = 0) => new Promise((resolve) => {
setTimeout(() => {
resolve(mockData);
}, time);
});
or a new Promise with a delayed .reject
const _returnError = (time = simulatedDelay) => {
const returnValue = new Promise(((resolve, reject) => {
setTimeout(() => {
reject(new Error('error'));
}, time);
}));
return returnValue;
};
but when I make my mock put call this returns a mock data that the calling method interprets as a success and console logs in its .then
put(target, putBody) {
const returnValue = _fetch(target, simulatedDelay)
returnValue.then(response => _console('PUT', target, response, putBody));
return returnValue;
},
But with an invalid target console logs an uncaught error
or this handles the error correctly, but console logs an undefined response
put(target, putBody) {
const returnValue = _fetch(target, simulatedDelay).then(response => _console('PUT', target, response, putBody));
return returnValue;
},
Here's the calling method:
saveStuff({ commit, state }, newStuff) {
//other code
return this.$mockAxios.put(url, putBody)
.then((response) => {
return response;
});
},
I feel like I'm completely missing something and I've researched this for hours and I'm still not getting it.

As a direct answer to the question: yes, you can add .then() to a promise after it's created.
Example:
const hi = new Promise((resolve, reject) => {
setTimeout(() => resolve('hello'), 2000);
});
hi.then(result => console.log(result));
As for promises baffling you, I would recommend (aside from more reading) just playing around a lot in your IDE with setTimeout. I know you're already using setTimeout in your mock, but strip it down further and just run the code in its own file, so that you control the whole environment. With lots of console.log('blah') to see the order and such. Also ensure you're just as familiar with callbacks, as promises are just syntactic sugar for callbacks. Try to read up on the JS event loop at the same time - it might provide some context if you know how and when a callback/promise executes.
Note that you can even add .then() after the callback has resolved or rejected. Hence the term "promise" - it's literally a promise that your .then() function will run. https://en.wikipedia.org/wiki/Promise_theory
const hi = new Promise((resolve, reject) => {
setTimeout(() => {
console.log('one second');
resolve();
}, 1000);
});
setTimeout(() => {
hi.then(() => console.log('two seconds. this executes approximately a full second after the first promise has resolved'));
}, 2000);

How to properly chain promises using reduce

I have a system that wants to create many folders in dropbox using the api, however i appear to attempt to create all the folders at once which causes errors to be generated, stating that i am performing too many write operations from dropbox.
My code is as follows and first uses reduce to create multiple promises which i thought were chained. In these promises the function add is called, which uploads the case to mongodb and then creates a dropbox folder for it, however this results in throttling errors..
bulkAdd: function (req, callback) {
issues = []
i = 1
req.reduce((promise, audit) => {
return promise.then(_ => this.add(audit, function(err,data){
if (err){
console.log('\n'+i+ ' ' + data.scanner_ui + '\n');
}
}));
}, Promise.resolve()).catch(error => {console.log(error)});
},
add: function (req, callback) {
delete req.status
var audit = new Audit(req);
if (req['status_value'] != undefined && req.status_value != ''){
console.log(req['status_value'])
audit.status = [{
status_value : req['status_value'],
status_notes : req['status_notes'],
status_date : req['status_date'],
}]
}
audit.save(function (err, data) {
if (err) {
callback(err, data)
}
else {
return dropbox_functions.createFolder(data.ui)
.then(response => {console.log(response)}, error=> {console.log('\n\n\n',error.error.error)})
.catch(error => console.log(error))
}
});
},

So the problem in your current question comes from the fact that your add function doesn't return a value, I only see it returning undefined.
If a promise returns something else than a promise in its then / catch block, it will use this input for the following function, and it will not wait for any internal processes to run through before finishing
If inside your then / catch blocks, you would return a promise, it would wait before continuing to the next then block, thus handling your requests sequential.
Now in your current code, I believe the easiest would be to handle the resolve inside your reduce, since you seem to be stuck with your callback handle already.
req.reduce((promise, audit) => {
return promise.then(_ => new Promise(
function( resolve, reject) {
this.add(audit, function(err,data){
if (err){
console.log('\n'+i+ ' ' + data.scanner_ui + '\n');
reject( err );
return;
}
resolve( data );
});
})
);
}, Promise.resolve()).catch(error => {console.log(error)});
in this case, the promise would either reject or resolve itself. I have chosen to submit err and data respectively, so this would be handled in the end in case an error occurs, and so that you can have the last data that got saved successfully

To properly chain you should make sure that you return a promise object.
Your reduce in the end creates a promise chain something like this.
Promise.resolve()
.then(() => {
console.log('setting up first timeout');
setTimeout(() => {
console.log("1 wait");
}, 2000);
})
.then(() => {
console.log('setting up second timeout');
setTimeout(() => {
console.log("2 wait");
}, 2000);
})
.catch(err => console.log("error", err));
If you run it, you'll see that it does not wait for one promise to end before moving down the chain.
Whereas, in the second example it waits for the first one to complete because a Promise object is returned by the first promise.
Promise.resolve()
.then(() => {
return new Promise(function(resolve, reject) {
console.log('setting up first timeout');
setTimeout(() => {
console.log("1 wait");
resolve();
}, 2000);
});
})
.then(() => {
return new Promise(function(resolve, reject) {
console.log('setting up second timeout');
setTimeout(() => {
console.log("2 wait");
resolve();
}, 2000);
});
})
.catch(err => console.log("error", err));
The difference is the first example is not returning Promise object. So, if you make sure each success handler returns a Promise object which is resolved only after your add function is done executing, you should be fine.

Unless there is a good reason for bulkAdd() to be written in nodeback style, you will find it more convenient to return a promise. The need for a nodeback will disappear and .reduce() will sit much more comfortably inside the function.
Using .reduce() and preserving nodeback style is possible but cumbersone, as it involves a rather ugly double-shuffle from nodeback to promise, and promise back to nodeback.
Assuming you are free to adapt the caller(s) to accept a returned promise, the code would be something like this :
'bulkAdd': function(req) {
return req.reduce((promise, audit) => {
return promise.then(_ => this.add(audit));
}, Promise.resolve());
},
'add': function(req) {
delete req.status;
var audit = new Audit(req);
if (req.status_value != undefined && req.status_value != '') {
audit.status = [{
'status_value': req.status_value,
'status_notes': req.status_notes,
'status_date': req.status_date
}];
}
return new Promise((resolve, reject) => { // in-line promisification of audit.save()
audit.save((err, data) => {
err ? reject(err) : resolve(data);
});
})
.then(data => dropbox_functions.createFolder(data.ui));
},
all catching and logging intentionally removed
The detail may differ, depending primarily on :
what data (if any) you want to be delivered to the caller
what you want to happen when errors occur.

Uncaught (in promise) error when testing promise with Mocha

I had hard times testing promise based functions. I am using Mocha as test framework and chai library for assertion framework. I new to both Mocha and chai. I had few problems and I do not know that is wrong with my code.Maybe my testing approach totally wrong, maybe someone help em.
I get Uncaught (in promise) error for expect, but actually I do not know whether my way is the correct way of testing these functions.
Here is my returnResult function which resolves a value -> a string
var returnResult = function (stateParamName, stateParamValue) {
return new Promise((resolve, reject) => {
peer3.get({ path: { equals: 'todo/#0' } }).then(function (results) {
console.log(stateParamName + ': ' + results[0].value[stateParamName])
resolve(results[0].value[stateParamName]);
});
});
}
And here is my mocha test
describe("Call Tests Suite", function () {
describe("Basic Call Test", function () {
it("Call status for both side should be IN CALL", function () {
peer3.call('login/add', ['testaccount1'])
.then(() => peer3.call('todo/makeCall1', ['testaccount2#testdomain.com']))
.then(() => checkResult('state_term', 'RINGING'))
.then((interval) => { clearInterval(interval); peer3.call('todo/answerCall2', ['empty']) })
.then(() => checkResult('state_term', 'IN_CALL'))
.then((interval) => clearInterval(interval))
//.then(console.log('test sonucu: ' + returnResult('state_term', 'IN_CALL')))
.then(returnResult('state_term', 'IN_CALL'))
.then((result) => expect(result).to.equal('IN_CALL'))
});
});
As you see I am only using assert for last result. Maybe I should test whole test as an promise function. Can someone help me on this ?

I don't know from where your error come from. However, there are a lot of things in your code you can improve, and may lead you to a better debugging, so you can find the error:
1- You should add a .catch handler at the end of the promise chain. The 'uncaught error' refers to this: you have an error in one of your then handlers but it is not caught in a catch. You should add a catch call at the end of the train:
describe("Call Tests Suite", function () {
describe("Basic Call Test", function () {
it("Call status for both side should be IN CALL", function () {
peer3.call('login/add', ['testaccount1'])
.then(() => peer3.call('todo/makeCall1', ['testaccount2#testdomain.com']))
.then(() => checkResult('state_term', 'RINGING'))
.then((interval) => { clearInterval(interval); peer3.call('todo/answerCall2', ['empty']) })
.then(() => checkResult('state_term', 'IN_CALL'))
.then((interval) => clearInterval(interval))
//.then(console.log('test sonucu: ' + returnResult('state_term', 'IN_CALL')))
.then(returnResult('state_term', 'IN_CALL'))
.then((result) => expect(result).to.equal('IN_CALL'))
.catch(err => {
console.log(err);//This will allow you better debugging.
})
});
});
Ok, now, we have to keep in mind that your code is asynchronous. However, mocha it functions, by default, are synchronous: they will not wait for your async code to execute.
In order to tell mocha that your test is asynchronous, you have to pass a parameter to the test. This parameter is a function, usually called done, that you must explicitly call when your test finish. Otherwise, your test will finish before reaching the asynchronous part of your code, usually giving you false positives.
describe("Call Tests Suite", function () {
describe("Basic Call Test", function () {
it("Call status for both side should be IN CALL", function (done) {
peer3.call('login/add', ['testaccount1'])
.then(() => peer3.call('todo/makeCall1', ['testaccount2#testdomain.com']))
.then(() => checkResult('state_term', 'RINGING'))
.then((interval) => { clearInterval(interval); peer3.call('todo/answerCall2', ['empty']) })
.then(() => checkResult('state_term', 'IN_CALL'))
.then((interval) => clearInterval(interval))
//.then(console.log('test sonucu: ' + returnResult('state_term', 'IN_CALL')))
.then(returnResult('state_term', 'IN_CALL'))
.then((result) => expect(result).to.equal('IN_CALL'))
.then( () => {
done(); //dont use .then(done) or things may break due to extra
parameter
})
.catch( err => {
console.log(err);
done(err); //passing a parameter to done makes the test fail.
})
});
});
Still, there are an issue with your code we must address. The then method expects a function as a parameter. However, in this line:
.then(returnResult('state_term', 'IN_CALL'))
You are passing it a call to returnResult('state_term', 'IN_CALL'), which return not a function, but a promise. You should pass a function instead -and then return the promise-:
.then(() => returnResult('state_term', 'IN_CALL')) //now the parameter to
//then is a function that return a Promise, not a Promise itself.
Also, as you've been told in the commments, you're explicitly returning a new Promise that wraps a Promise in your return result function: that is not needed at all and that function could be written as so:
var returnResult = function (stateParamName, stateParamValue) {
return peer3.get({ path: { equals: 'todo/#0' } }).then(function (results) {
console.log(stateParamName + ': ' + results[0].value[stateParamName]);
return(results[0].value([stateParamName]));
});
}
However, there are a lot of things in your code that seems really odd (I'am not sure at all why the setinterval calls are there), so I'm pretty confident the test will not work as you expect. You should start by familiarizing yourself with Promises and asynchronous mocha tests, and don't try to test really long sequences of asynchronous operations. good luck!