Michael Bryan

Michael Bryan

1570034162

JavaScript Promises: The Definitive Guide, Part 1

The single-threaded, event-loop based concurrency model of JavaScript deals with processing of events using so-called “asynchronous non-blocking I/O model.” Unlike computer languages such as Java, where events are handled using additional threads and processed in parallel with the main execution thread, JavaScript code is executed sequentially. In order to prevent blocking the main thread on I/O-bound operations, JavaScript uses a callback mechanism where asynchronous operations specify a callback – the function to be executed when the result of an asynchronous operation is ready; while the code control flow continues executing.

Whenever we want to use the result of a callback to make another asynchronous call, we need to nest callbacks. Since I/O operations can result in errors, we need to handle errors for each callback before processing the success result. This necessity to do error handling and having to embed callbacks makes the callback code difficult to read. Sometimes this is referred to as “JavaScript callback hell.”

In order to address this problem, JavaScript offers a mechanism called a Promise. It is a common programming paradigm (more about it here: https://en.wikipedia.org/wiki/Futures_and_promises) and TC39 introduced it in ECMAScript 2015. The JavaScript Promise is an object holding a state, which represents an eventual completion (or failure) of an asynchronous operation and its resulting value.

A new Promise is in the pending state. If a Promise succeeds it is put in a resolved state otherwise it is rejected. Instead of using the original callback mechanism, code using Promises creates a Promise object. We use Promises typically with two callback handlers – resolved invoked when the operation was successful and rejected called whenever an error has occurred.

// Converting a callback based method to a method that returns Promise
const fs = require('fs')

const readTextFromFile = new Promise((resolve, reject) => {
  fs.readFile('file.txt', (err, data) => {
    if (err) {
      return reject(err)
    }

    resolve(data)
  })
})

// Usage of a method that returns Promise
readTextFromFile()
  .then(data => console.log(data))
  .catch(e => console.log(e))

Process.nextTick(callback)

To understand how Promises work in Node.js, it is important to review how process.nextTick() works in Node.js, as the two are very similar. Process.nextTick() is a method that adds a callback to the “next tick queue.” Tasks in the queue are executed after the current operation in the event loop is done and before the event loop is allowed to continue. Simply said, there’s another queue beside the event loop that we can use to schedule events. This queue is even faster than the event loop and it may be drained several times in a single event loop tick.

const log = msg => () => console.log(`NEXT TICK ${msg}`)

const timeout = (time, msg) => {
  setTimeout(() => {
    console.log(`TIMEOUT ${msg}`)
  }, time)
}

process.nextTick(log('ONE'))
timeout(0, 'AFTER-ONE')
process.nextTick(log('TWO'))
timeout(0, 'AFTER-TWO')

In the example above, we can see how process.nextTick works in practice. We have two setTimeout calls, with callbacks immediately scheduled in the event loop. We also have two process.nextTick methods with callbacks scheduled in the “next tick queue.” This is what we see in the console:

Next TICK ONE
Next TICK TWO
TIMEOUT AFTER-ONE
TIMEOUT AFTER-TWO

Since we know that “next tick queue” is separate from event loop and can be drained multiple times in a single event loop tick, this makes sense. Two nextTick callbacks are executed immediately and the other two setTimeout callbacks, set in the event loop, are executed after.

Putting so many callbacks in the “next tick queue” may block the event loop and prevent any I/O operation. That’s why we have process.maxTickDepth that represents the maximum number of callbacks in the queue that can be executed before allowing the event loop to continue. Its default value is 1000.

How Do Promises Work?

Promises are a new and nice way to handle async code, but how do they really work? For understanding the benefits and the performance characteristics of Promises we need to understand how they are implemented and what really happens when we return new Promise() .

Promises use the Microtask queue and they are executed independently from regular tasks (the setTimeout callback, for example). What does this really mean? In JavaScript, we have three queues: (1) event loop, (2) nextTick queue and (3) Microtask queue. All those queues work independently.

Macrotasks are regular tasks that are going into the event loop and in one event loop tick, only one Macrotask is executed. Microtasks have an independent queue and, in one event-loop tick, the whole microtasks queue can be drained. This gives us a really good performance benefit. Basically, we use microtasks when we need to do stuff asynchronously in a synchronous way, as fast as possible.

Promises are executed as Microtasks. This means that they are executed sooner than Macrotasks. They are never executed concurrently. Microtasks are always executed sequentially, so talking about parallelism with Promises is wrong. They work like process.nextTick, independently from event loop in their own microtask queue.

Macrotasks: setTimeout, setInterval, setImmediate, requestAnimationFrame, I/O, UI rendering

Microtasks: process.nextTick, Promises, Object.observe, MutationObserver (read more here)

const fetch = require('node-fetch') // only when running in Node.js

const fetchData = fetch('https://api.github.com/users/nearform/repos')
  .then(() => console.log('Hi from fetch!'))
  .catch(e => console.error(e))

console.log('Hi!')

setTimeout(() => {
  console.log('Hi from setTimeout')
}, 0)

fetchData()

In the example above, the code in the Promise will be scheduled in the Microtask queue, but since that action requires the network, it will only be resolved after the data is received. In this example, we’ll see this output:

Hi!
Hi from setTimeout!
Hi from fetch

We also need to mention that the timing of callbacks and Promises can vary significantly depending on the environment (browser or Node.js).

Promise Methods

Promise.all(iterable)

It takes an array of Promises and returns a Promise that either fulfills when all of the Promises in the iterable argument have been fulfilled or rejects as soon as one of the Promises rejects. If the returned Promise fulfills, it’s fulfilled with an array of the values from the fulfilled Promises in the same order as defined in the array argument. If the returned Promise rejects, it is rejected with the reason from the first Promise in the array that got rejected. This method can be useful for aggregating results of multiple Promises.

The biggest confusion about Promise.all is that Promises passed in the iterable are executed concurrently. Promise.all doesn’t provide parallelism! The function passed in the Promise constructor is executed immediately and Promise is resolved in the microtask queue. Microtasks are always executed in sequence.

This method is useful when we want to wait for multiple Promises to resolve (or reject) without manually chaining them. The most common use case is mapping through an array and returning a Promise for every element:

const results = await Promise.all(

 items.map(item => generateResultFromItem(item))

)

The first rejection of a Promise will cause Promise.all() to reject, but other constituent Promises will still be executing. This can be harmful as we will be using resources for generating results that won’t be used.

const util = require('util')
const sleep = util.promisify(setTimeout)

Promise.all([
  sleep(1000).then(() => console.log('b')),
  Promise.reject('a')
]).catch((err) => console.log(err))

In the example above, we’re passing two Promises in Promise.all(). The first one is waiting one second and then logging letter b in the console. The second one is rejected with the letter a. Since the second one is rejected, we would expect to see only a in the console, but you’ll see **a **and b. That’s because you can’t cancel the Promise. Every scheduled Promise will be executed and Promise.all just helps us to ignore the result if one of the Promises in the iterable is rejected, and gives us a rejected Promise as a result.

Promise.race(iterable)

It takes an array of Promises and executes them in the same way as Promise.all, the difference being it returns a Promise that fulfills or rejects as soon as one of the Promises in the iterable fulfills or rejects, with the value or reason from that Promise. As an example, Promise.race can be used for building a timeout functionality, where the first Promise will be an HTTP request to some service, and a second one will be a timeout function. If the second one fails first, the resulting Promise from Promise.race() will be rejected and the data from the first Promise won’t be available. The rejection of one Promise from the iterable won’t cancel others, they will be still be executed, as in the Promise.all method case.

const fetch = require('node-fetch') // only when running in Node.js

const getUserRepos = () =>
 fetch('https://api.github.com/users/nearform/repos')

const timeout = delay =>
  new Promise((resolve, reject) => {
    setTimeout(() => reject(new Error('request timeout')), delay)
  })

Promise.race([getUserRepos(), timeout(300)])
  .then(repos => console.log(repos))
  .catch(e => console.error(e))

Promise.reject(reason)

Returns a Promise object that is rejected with the given reason as an argument. It is mainly used to throw an error in the Promise chain.

Promise.resolve(value)

Returns a Promise that is resolved with the given value as an argument. It is mainly used to cast a value into the Promise, some object or array, so we can chain it later with other async code.

Async/Await

Async/await semantics were added in ECMAScript 2017, allowing programmers to deal with Promises in a more intuitive way. The word “async” before a function means one simple thing: a function always returns a Promise. If the code has returned in it, then JavaScript automatically wraps it into a resolved Promise with that value. The keyword await, which can only occur inside an async function, makes JavaScript wait until the Promise has been settled and returns its result.

Below is a function waiting on a Promise that is resolved after one second using async/await keywords:

let promise = new Promise((resolve, reject) => {
  setTimeout(() => resolve("done!"), 1000)
})

async function f() {
  let result = await promise // wait till the Promise resolves
  alert(result) // "done!"
}

That’s all for Part 1! Tune in on Monday when we’ll discuss common mistakes with promises.

Originally published by Ivan Jovanovic at https://dzone.com

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☞ Complete JavaScript Course For Beginners to Master - 2019

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JavaScript Promises: The Definitive Guide, Part 1

A Wrapper for Sembast and SQFlite to Enable Easy

FHIR_DB

This is really just a wrapper around Sembast_SQFLite - so all of the heavy lifting was done by Alex Tekartik. I highly recommend that if you have any questions about working with this package that you take a look at Sembast. He's also just a super nice guy, and even answered a question for me when I was deciding which sembast version to use. As usual, ResoCoder also has a good tutorial.

I have an interest in low-resource settings and thus a specific reason to be able to store data offline. To encourage this use, there are a number of other packages I have created based around the data format FHIR. FHIR® is the registered trademark of HL7 and is used with the permission of HL7. Use of the FHIR trademark does not constitute endorsement of this product by HL7.

Using the Db

So, while not absolutely necessary, I highly recommend that you use some sort of interface class. This adds the benefit of more easily handling errors, plus if you change to a different database in the future, you don't have to change the rest of your app, just the interface.

I've used something like this in my projects:

class IFhirDb {
  IFhirDb();
  final ResourceDao resourceDao = ResourceDao();

  Future<Either<DbFailure, Resource>> save(Resource resource) async {
    Resource resultResource;
    try {
      resultResource = await resourceDao.save(resource);
    } catch (error) {
      return left(DbFailure.unableToSave(error: error.toString()));
    }
    return right(resultResource);
  }

  Future<Either<DbFailure, List<Resource>>> returnListOfSingleResourceType(
      String resourceType) async {
    List<Resource> resultList;
    try {
      resultList =
          await resourceDao.getAllSortedById(resourceType: resourceType);
    } catch (error) {
      return left(DbFailure.unableToObtainList(error: error.toString()));
    }
    return right(resultList);
  }

  Future<Either<DbFailure, List<Resource>>> searchFunction(
      String resourceType, String searchString, String reference) async {
    List<Resource> resultList;
    try {
      resultList =
          await resourceDao.searchFor(resourceType, searchString, reference);
    } catch (error) {
      return left(DbFailure.unableToObtainList(error: error.toString()));
    }
    return right(resultList);
  }
}

I like this because in case there's an i/o error or something, it won't crash your app. Then, you can call this interface in your app like the following:

final patient = Patient(
    resourceType: 'Patient',
    name: [HumanName(text: 'New Patient Name')],
    birthDate: Date(DateTime.now()),
);

final saveResult = await IFhirDb().save(patient);

This will save your newly created patient to the locally embedded database.

IMPORTANT: this database will expect that all previously created resources have an id. When you save a resource, it will check to see if that resource type has already been stored. (Each resource type is saved in it's own store in the database). It will then check if there is an ID. If there's no ID, it will create a new one for that resource (along with metadata on version number and creation time). It will save it, and return the resource. If it already has an ID, it will copy the the old version of the resource into a _history store. It will then update the metadata of the new resource and save that version into the appropriate store for that resource. If, for instance, we have a previously created patient:

{
    "resourceType": "Patient",
    "id": "fhirfli-294057507-6811107",
    "meta": {
        "versionId": "1",
        "lastUpdated": "2020-10-16T19:41:28.054369Z"
    },
    "name": [
        {
            "given": ["New"],
            "family": "Patient"
        }
    ],
    "birthDate": "2020-10-16"
}

And we update the last name to 'Provider'. The above version of the patient will be kept in _history, while in the 'Patient' store in the db, we will have the updated version:

{
    "resourceType": "Patient",
    "id": "fhirfli-294057507-6811107",
    "meta": {
        "versionId": "2",
        "lastUpdated": "2020-10-16T19:45:07.316698Z"
    },
    "name": [
        {
            "given": ["New"],
            "family": "Provider"
        }
    ],
    "birthDate": "2020-10-16"
}

This way we can keep track of all previous version of all resources (which is obviously important in medicine).

For most of the interactions (saving, deleting, etc), they work the way you'd expect. The only difference is search. Because Sembast is NoSQL, we can search on any of the fields in a resource. If in our interface class, we have the following function:

  Future<Either<DbFailure, List<Resource>>> searchFunction(
      String resourceType, String searchString, String reference) async {
    List<Resource> resultList;
    try {
      resultList =
          await resourceDao.searchFor(resourceType, searchString, reference);
    } catch (error) {
      return left(DbFailure.unableToObtainList(error: error.toString()));
    }
    return right(resultList);
  }

You can search for all immunizations of a certain patient:

searchFunction(
        'Immunization', 'patient.reference', 'Patient/$patientId');

This function will search through all entries in the 'Immunization' store. It will look at all 'patient.reference' fields, and return any that match 'Patient/$patientId'.

The last thing I'll mention is that this is a password protected db, using AES-256 encryption (although it can also use Salsa20). Anytime you use the db, you have the option of using a password for encryption/decryption. Remember, if you setup the database using encryption, you will only be able to access it using that same password. When you're ready to change the password, you will need to call the update password function. If we again assume we created a change password method in our interface, it might look something like this:

class IFhirDb {
  IFhirDb();
  final ResourceDao resourceDao = ResourceDao();
  ...
    Future<Either<DbFailure, Unit>> updatePassword(String oldPassword, String newPassword) async {
    try {
      await resourceDao.updatePw(oldPassword, newPassword);
    } catch (error) {
      return left(DbFailure.unableToUpdatePassword(error: error.toString()));
    }
    return right(Unit);
  }

You don't have to use a password, and in that case, it will save the db file as plain text. If you want to add a password later, it will encrypt it at that time.

General Store

After using this for a while in an app, I've realized that it needs to be able to store data apart from just FHIR resources, at least on occasion. For this, I've added a second class for all versions of the database called GeneralDao. This is similar to the ResourceDao, but fewer options. So, in order to save something, it would look like this:

await GeneralDao().save('password', {'new':'map'});
await GeneralDao().save('password', {'new':'map'}, 'key');

The difference between these two options is that the first one will generate a key for the map being stored, while the second will store the map using the key provided. Both will return the key after successfully storing the map.

Other functions available include:

// deletes everything in the general store
await GeneralDao().deleteAllGeneral('password'); 

// delete specific entry
await GeneralDao().delete('password','key'); 

// returns map with that key
await GeneralDao().find('password', 'key'); 

FHIR® is a registered trademark of Health Level Seven International (HL7) and its use does not constitute an endorsement of products by HL7®

Use this package as a library

Depend on it

Run this command:

With Flutter:

 $ flutter pub add fhir_db

This will add a line like this to your package's pubspec.yaml (and run an implicit flutter pub get):

dependencies:
  fhir_db: ^0.4.3

Alternatively, your editor might support or flutter pub get. Check the docs for your editor to learn more.

Import it

Now in your Dart code, you can use:

import 'package:fhir_db/dstu2.dart';
import 'package:fhir_db/dstu2/fhir_db.dart';
import 'package:fhir_db/dstu2/general_dao.dart';
import 'package:fhir_db/dstu2/resource_dao.dart';
import 'package:fhir_db/encrypt/aes.dart';
import 'package:fhir_db/encrypt/salsa.dart';
import 'package:fhir_db/r4.dart';
import 'package:fhir_db/r4/fhir_db.dart';
import 'package:fhir_db/r4/general_dao.dart';
import 'package:fhir_db/r4/resource_dao.dart';
import 'package:fhir_db/r5.dart';
import 'package:fhir_db/r5/fhir_db.dart';
import 'package:fhir_db/r5/general_dao.dart';
import 'package:fhir_db/r5/resource_dao.dart';
import 'package:fhir_db/stu3.dart';
import 'package:fhir_db/stu3/fhir_db.dart';
import 'package:fhir_db/stu3/general_dao.dart';
import 'package:fhir_db/stu3/resource_dao.dart'; 

example/lib/main.dart

import 'package:fhir/r4.dart';
import 'package:fhir_db/r4.dart';
import 'package:flutter/material.dart';
import 'package:test/test.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();

  final resourceDao = ResourceDao();

  // await resourceDao.updatePw('newPw', null);
  await resourceDao.deleteAllResources(null);

  group('Playing with passwords', () {
    test('Playing with Passwords', () async {
      final patient = Patient(id: Id('1'));

      final saved = await resourceDao.save(null, patient);

      await resourceDao.updatePw(null, 'newPw');
      final search1 = await resourceDao.find('newPw',
          resourceType: R4ResourceType.Patient, id: Id('1'));
      expect(saved, search1[0]);

      await resourceDao.updatePw('newPw', 'newerPw');
      final search2 = await resourceDao.find('newerPw',
          resourceType: R4ResourceType.Patient, id: Id('1'));
      expect(saved, search2[0]);

      await resourceDao.updatePw('newerPw', null);
      final search3 = await resourceDao.find(null,
          resourceType: R4ResourceType.Patient, id: Id('1'));
      expect(saved, search3[0]);

      await resourceDao.deleteAllResources(null);
    });
  });

  final id = Id('12345');
  group('Saving Things:', () {
    test('Save Patient', () async {
      final humanName = HumanName(family: 'Atreides', given: ['Duke']);
      final patient = Patient(id: id, name: [humanName]);
      final saved = await resourceDao.save(null, patient);

      expect(saved.id, id);

      expect((saved as Patient).name?[0], humanName);
    });

    test('Save Organization', () async {
      final organization = Organization(id: id, name: 'FhirFli');
      final saved = await resourceDao.save(null, organization);

      expect(saved.id, id);

      expect((saved as Organization).name, 'FhirFli');
    });

    test('Save Observation1', () async {
      final observation1 = Observation(
        id: Id('obs1'),
        code: CodeableConcept(text: 'Observation #1'),
        effectiveDateTime: FhirDateTime(DateTime(1981, 09, 18)),
      );
      final saved = await resourceDao.save(null, observation1);

      expect(saved.id, Id('obs1'));

      expect((saved as Observation).code.text, 'Observation #1');
    });

    test('Save Observation1 Again', () async {
      final observation1 = Observation(
          id: Id('obs1'),
          code: CodeableConcept(text: 'Observation #1 - Updated'));
      final saved = await resourceDao.save(null, observation1);

      expect(saved.id, Id('obs1'));

      expect((saved as Observation).code.text, 'Observation #1 - Updated');

      expect(saved.meta?.versionId, Id('2'));
    });

    test('Save Observation2', () async {
      final observation2 = Observation(
        id: Id('obs2'),
        code: CodeableConcept(text: 'Observation #2'),
        effectiveDateTime: FhirDateTime(DateTime(1981, 09, 18)),
      );
      final saved = await resourceDao.save(null, observation2);

      expect(saved.id, Id('obs2'));

      expect((saved as Observation).code.text, 'Observation #2');
    });

    test('Save Observation3', () async {
      final observation3 = Observation(
        id: Id('obs3'),
        code: CodeableConcept(text: 'Observation #3'),
        effectiveDateTime: FhirDateTime(DateTime(1981, 09, 18)),
      );
      final saved = await resourceDao.save(null, observation3);

      expect(saved.id, Id('obs3'));

      expect((saved as Observation).code.text, 'Observation #3');
    });
  });

  group('Finding Things:', () {
    test('Find 1st Patient', () async {
      final search = await resourceDao.find(null,
          resourceType: R4ResourceType.Patient, id: id);
      final humanName = HumanName(family: 'Atreides', given: ['Duke']);

      expect(search.length, 1);

      expect((search[0] as Patient).name?[0], humanName);
    });

    test('Find 3rd Observation', () async {
      final search = await resourceDao.find(null,
          resourceType: R4ResourceType.Observation, id: Id('obs3'));

      expect(search.length, 1);

      expect(search[0].id, Id('obs3'));

      expect((search[0] as Observation).code.text, 'Observation #3');
    });

    test('Find All Observations', () async {
      final search = await resourceDao.getResourceType(
        null,
        resourceTypes: [R4ResourceType.Observation],
      );

      expect(search.length, 3);

      final idList = [];
      for (final obs in search) {
        idList.add(obs.id.toString());
      }

      expect(idList.contains('obs1'), true);

      expect(idList.contains('obs2'), true);

      expect(idList.contains('obs3'), true);
    });

    test('Find All (non-historical) Resources', () async {
      final search = await resourceDao.getAll(null);

      expect(search.length, 5);
      final patList = search.toList();
      final orgList = search.toList();
      final obsList = search.toList();
      patList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Patient);
      orgList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Organization);
      obsList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Observation);

      expect(patList.length, 1);

      expect(orgList.length, 1);

      expect(obsList.length, 3);
    });
  });

  group('Deleting Things:', () {
    test('Delete 2nd Observation', () async {
      await resourceDao.delete(
          null, null, R4ResourceType.Observation, Id('obs2'), null, null);

      final search = await resourceDao.getResourceType(
        null,
        resourceTypes: [R4ResourceType.Observation],
      );

      expect(search.length, 2);

      final idList = [];
      for (final obs in search) {
        idList.add(obs.id.toString());
      }

      expect(idList.contains('obs1'), true);

      expect(idList.contains('obs2'), false);

      expect(idList.contains('obs3'), true);
    });

    test('Delete All Observations', () async {
      await resourceDao.deleteSingleType(null,
          resourceType: R4ResourceType.Observation);

      final search = await resourceDao.getAll(null);

      expect(search.length, 2);

      final patList = search.toList();
      final orgList = search.toList();
      patList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Patient);
      orgList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Organization);

      expect(patList.length, 1);

      expect(patList.length, 1);
    });

    test('Delete All Resources', () async {
      await resourceDao.deleteAllResources(null);

      final search = await resourceDao.getAll(null);

      expect(search.length, 0);
    });
  });

  group('Password - Saving Things:', () {
    test('Save Patient', () async {
      await resourceDao.updatePw(null, 'newPw');
      final humanName = HumanName(family: 'Atreides', given: ['Duke']);
      final patient = Patient(id: id, name: [humanName]);
      final saved = await resourceDao.save('newPw', patient);

      expect(saved.id, id);

      expect((saved as Patient).name?[0], humanName);
    });

    test('Save Organization', () async {
      final organization = Organization(id: id, name: 'FhirFli');
      final saved = await resourceDao.save('newPw', organization);

      expect(saved.id, id);

      expect((saved as Organization).name, 'FhirFli');
    });

    test('Save Observation1', () async {
      final observation1 = Observation(
        id: Id('obs1'),
        code: CodeableConcept(text: 'Observation #1'),
        effectiveDateTime: FhirDateTime(DateTime(1981, 09, 18)),
      );
      final saved = await resourceDao.save('newPw', observation1);

      expect(saved.id, Id('obs1'));

      expect((saved as Observation).code.text, 'Observation #1');
    });

    test('Save Observation1 Again', () async {
      final observation1 = Observation(
          id: Id('obs1'),
          code: CodeableConcept(text: 'Observation #1 - Updated'));
      final saved = await resourceDao.save('newPw', observation1);

      expect(saved.id, Id('obs1'));

      expect((saved as Observation).code.text, 'Observation #1 - Updated');

      expect(saved.meta?.versionId, Id('2'));
    });

    test('Save Observation2', () async {
      final observation2 = Observation(
        id: Id('obs2'),
        code: CodeableConcept(text: 'Observation #2'),
        effectiveDateTime: FhirDateTime(DateTime(1981, 09, 18)),
      );
      final saved = await resourceDao.save('newPw', observation2);

      expect(saved.id, Id('obs2'));

      expect((saved as Observation).code.text, 'Observation #2');
    });

    test('Save Observation3', () async {
      final observation3 = Observation(
        id: Id('obs3'),
        code: CodeableConcept(text: 'Observation #3'),
        effectiveDateTime: FhirDateTime(DateTime(1981, 09, 18)),
      );
      final saved = await resourceDao.save('newPw', observation3);

      expect(saved.id, Id('obs3'));

      expect((saved as Observation).code.text, 'Observation #3');
    });
  });

  group('Password - Finding Things:', () {
    test('Find 1st Patient', () async {
      final search = await resourceDao.find('newPw',
          resourceType: R4ResourceType.Patient, id: id);
      final humanName = HumanName(family: 'Atreides', given: ['Duke']);

      expect(search.length, 1);

      expect((search[0] as Patient).name?[0], humanName);
    });

    test('Find 3rd Observation', () async {
      final search = await resourceDao.find('newPw',
          resourceType: R4ResourceType.Observation, id: Id('obs3'));

      expect(search.length, 1);

      expect(search[0].id, Id('obs3'));

      expect((search[0] as Observation).code.text, 'Observation #3');
    });

    test('Find All Observations', () async {
      final search = await resourceDao.getResourceType(
        'newPw',
        resourceTypes: [R4ResourceType.Observation],
      );

      expect(search.length, 3);

      final idList = [];
      for (final obs in search) {
        idList.add(obs.id.toString());
      }

      expect(idList.contains('obs1'), true);

      expect(idList.contains('obs2'), true);

      expect(idList.contains('obs3'), true);
    });

    test('Find All (non-historical) Resources', () async {
      final search = await resourceDao.getAll('newPw');

      expect(search.length, 5);
      final patList = search.toList();
      final orgList = search.toList();
      final obsList = search.toList();
      patList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Patient);
      orgList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Organization);
      obsList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Observation);

      expect(patList.length, 1);

      expect(orgList.length, 1);

      expect(obsList.length, 3);
    });
  });

  group('Password - Deleting Things:', () {
    test('Delete 2nd Observation', () async {
      await resourceDao.delete(
          'newPw', null, R4ResourceType.Observation, Id('obs2'), null, null);

      final search = await resourceDao.getResourceType(
        'newPw',
        resourceTypes: [R4ResourceType.Observation],
      );

      expect(search.length, 2);

      final idList = [];
      for (final obs in search) {
        idList.add(obs.id.toString());
      }

      expect(idList.contains('obs1'), true);

      expect(idList.contains('obs2'), false);

      expect(idList.contains('obs3'), true);
    });

    test('Delete All Observations', () async {
      await resourceDao.deleteSingleType('newPw',
          resourceType: R4ResourceType.Observation);

      final search = await resourceDao.getAll('newPw');

      expect(search.length, 2);

      final patList = search.toList();
      final orgList = search.toList();
      patList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Patient);
      orgList.retainWhere(
          (resource) => resource.resourceType == R4ResourceType.Organization);

      expect(patList.length, 1);

      expect(patList.length, 1);
    });

    test('Delete All Resources', () async {
      await resourceDao.deleteAllResources('newPw');

      final search = await resourceDao.getAll('newPw');

      expect(search.length, 0);

      await resourceDao.updatePw('newPw', null);
    });
  });
} 

Download Details:

Author: MayJuun

Source Code: https://github.com/MayJuun/fhir/tree/main/fhir_db

#sqflite  #dart  #flutter 

Best Review

1629825646

Design Beast Review & OTO Link

Design Beast Review & OTOs + $20k Bonuses

CHECK BONUSES & GRAB IT AT: https://bit.ly/3yhtcqi

Welcome to my Design Beast Review A Very warm welcome to my DesignBeast Review Here You Will Find Honest Opinion About The Design Beast Whether It is A Right Fit For You or not also I Have Covered All Working processes of DesignBeast, Live Video Demo, features Pros & Cons & All Design Beast OTO details.

Govind Rana Here Stay Till the End Of This Review I Have included $20k Bonuses At the end Of DesignBeast Review

DesignBeast Review – World finest graphic designing & animation software that will come into existence in some days. If you are searching for DesignBeast Review then this is the right platform to get in-depth information and the truth for Design Beast Review. An AI-based designing software that enables the 3D designing technology to you.

I am pretty much excited to share my point of view about the design beast. and this is because I want to meet you to the high technology graphics software.

This software is going to launch on 26 Aug. 2021 by the very famous vendor Paul Ponna and this time he is launching is 2 years of efforts on this amazing app. So do believe me without any doubt, here I only share the actual facts for Designbeast Review.

At this time the limited information is available on the web so I have included the creator of DesignBeast, Paul Ponna’s previous launches, what is DesignBeast, features & benefits, examples, who will best fit for this app, pros & cons, included with a huge bonuses.

Discount will be rolling out from 26th August

(fingers crossed till its launch because it is the launch beyond expectations)

Design Beast Review – Overview

  • Creator: Paul Ponna
  • Product Name: DesignBeast
  • Launch Date – 2021-Aug-24
  • Launch Timing – 11:00 EDT
  • Pricing – $67
  • Official Website – Visit
  • Money-Back Guarantee- Information Not Available
  • Category – Graphic Designing
  • Training – Yes, Available
  • Bonuses – Techevoke Special Bonuses Available

About Paul Ponna the vendor & Creator of DesignBeast

Paul Ponna is an entrepreneur and a digital geek in the internet marketing niche. His previous launches were hit the market products and were evergreen. No comparison of his products because he knows what is a need in today’s market and how online marketers will get benefited from online technologies.

So let’s have a look at Paul Ponna’s previous hits in the saas industry.

  1. DoodleMaker – This is the doodle video maker and the popular software on JVZoo that is the biggest launch in the history of internet marketing software. With a doodle maker, you can create studio-quality doodle videos with this application.
  2. VideoCreator – A readymade video editing app that is more authentic than existing video editing software. No more templates creation is required and no extra efforts to make and you can make exciting effects with videocreator.
  3. There is more software that has been launched by Paul Ponna…
  • DoodleMaker
  • Avatar Builder
  • VideoCreator
  • DesignBeast (available on 26th Aug)

Paul Ponna is a tech entrepreneur and he was started his journey from his 18 and with a website and hosting spending only $20. And he is a millionaire and frequently launches products that are really amazing and useful.

So not further delays let come to the designbeast review and let’s talk about what will be this software and how can you get benefited from this.

What is Design Beast?

Design beast is a software that comes with 6 world-class designing technology, and with those 6 modules, you can fulfill your graphics needs in just 1 price tag.

DesignBeast is a software that is responsible for multipurpose designs and better technology including these below-mentioned modules.

  1. Design Automation App #1– All in One Design and Mockup Engine
  2. Design Automation App #1– 3D Live Motion Photos
  3. Design Automation App #1– Magic Object Remover
  4. Design Automation App #1– 1-Click Background Removal
  5. Design Automation App #1– Slick Image Editor
  6. Design Automation App #1– AI Logo Creator

This is app bundle is fully loaded with advanced graphics features that are essential for making high-quality posts, infographics, motion pictures, 3D banners, and more.

Here are all modules explanations of DesignBeast

So this is clear this app has various technologies that are responsible for advanced editing and professional graphical designs. So here is the module’s explanation.

  1. All in One Design and mockup Engine

This is a designs library, not an ordinary image or premade design library. All elements are customizable and you can create any of your imagination with this design and mockup engine.

7000+ ready-to-use customizable designs and mockups are available in this module. Just head over to the DesignBeast software and you will get the professional DFY designs and mockups for your graphics need.

There are for all social apps, means available in various sizes.

2. 3D Live Motion Photos

Now you can convert a still, boring photo to a live, 3D effect photo with the A.I. technology of DesignBeast. With this effect, you can engage with your audience in a more effective manner.

And you all know that a moving object with a visual effect is 10x more engaging than an ordinary graphical image. with this technology, you can grab the attention of your customers and get more clicks on your sales platform.

3. Magic Object Removal Tool

Most of the time we need to remove some object or any person from any of the selected images and this module will give you access to select the required object or person and the remove that thing is just one click.

The feature Paul Ponna offers in his software is rarely available on any other software. With only one click the magic happens and the object will be removed.

4. 1-Click Background Removal

Because the software has technology that is based on AI and Machine Learning. So it auto-detects the edges and objects in your photos and automatically erases the background from any photo.

You don’t need to make extra effects just select the 1 click background removal option and click on the image background and it will vanish within seconds.

5. Slick Image Editor

This has the multi-feature of basic editing for any photo. Just like edit, crop, short, effects, blur, and more. You don’t need to go for different apps to perform different tasks every time.

You can convert any still normal photo to a high-class visual and ready-to-use, ready-to-print photo with this module.

6. Artificial Intelligence Logo Creator

An AI logo creator, not just a free tool that is available in the online market but it is quite effective and useful for you to generate any kind of logo. You can now bulk-create 50 logo variations for any brand in 3 easy steps.

All designs are fully customizable, also a single object is customizable with this app.

How DesignBeast will fire in the saas market?

In this section of DesignBeast Review, I am sharing its popularity, hype, and the vendor name-fame with you, so that you can evaluate its worth.

Just because you need a better, time-saving, authentic, graphic designing and animation software that will fulfill your professional graphics need for online marketing.

Because paul Ponna is a tech entrepreneur and he knows what is write to tab the market and what should be the next useful tool for every marketer.

DesignBeast is now going to be a popular one from the software list of its vendor. No matter what competitors of DesignBeast will say about this software. But as a consumer and a digital marketer, I am pretty much excited for its official launch.

DesignBeast Features & Benefits

If you want to create designs for Social media, websites, e-commerce sites, local businesses, promos, and advertising then focus on the features & benefits of DesignBeast Review, so that you can evaluate its actual strength.

 A.I. & Machine Learning Technology

This is the platform that suggests automatically the designs, objects, effects & more things that are based on your needs and the design frame you choose.

Automate design tasks with machine learning and artificial intelligence to leapfrog your competition and maximize revenues.

 6 Apps in the Price of One

There is no comparison of this app in the online market because the bundle of 6 apps and those apps are highly authentic useful in today’s competitive marketing world.

You can replace multiple graphics apps from one that is DesignBeast and you need to replace it if you want to save your money and time.

 Multilingual

This app is available in multi-languages, and with this feature, it doesn’t matter from where you are in this world.

It enables you to sell your service towards the globe and also give you the access to create graphical content in your local language.

 Commercial and resell rights available

Commercial licensing brings you to another stage of selling your services to clients. Now you can freely sell all generated content to your clients in the market. Also charge extra fees according to your skills and set your service on commercial platforms.

 Copywrite free assets and resources

Assets that are really expensive and everyone even I needs to purchase from the online market and those services are very expensive for all of us. But now all are available at one place that is design beast, you will get premium royalty-free images, icons, backgrounds & animations.

 Save Time and money

You can build world-class designs in minutes and all designs are professional, in starting you need to learn some lessons and practice to perform with DesignBeast membersarea.

 Dynamic Visual Effects

The effects offered by this software is so amazing and fully customizable so that I have given the term dynamic. All things are editable and ready to use.

Is there are any skills required to work with DesignBeast?

Designbeast is a DFY editable templates advanced graphic design software that will suggest to you the designs from its A.I. and machine learning technology. So I am sure you don’t need any advanced skills to use DesignBeast.

But to be honest, you need to work on these soft skills.

  1. Knowledge of using basic online apps.
  2. The mindset to Selecting the best
  3. Knowledge of colors
  4. Knowledge of graphics
  5. Understanding of designs
  6. Branding

And there are most soft skills required.

Design Beast Review – Who will be fit for this software?

So now in this series, it’s time to share the industry people who are best fit for this software that is Designbeast. And after lots of research and analysis, I decided to include these professionals in the DesignBeast audience. I am happy to share my point views in this DesignBeast Review.

  • Graphic Designers
  • Digital Marketers
  • Bloggers.
  • Vloggers
  • Youtubers
  • Media Agency
  • Advertising agency
  • Local Businesses
  • Ecommerce Players

DesignBeast Review – Pros & Cons

I have shared the sure short pros and cons for this revolutionary software. But there are some cons also available. After reviewing the product, as a marketer, I also realized this has lots of pros and some cons available in the market.

Pros

  • 6 modules in 1 app
  • 3d photo creation technology with AI and machine learning
  • Background and object removal technology.
  • Designs library over 7000
  • Kindly support team.
  • Trustable vendor
  • 30 Days money back gaurantee.
  • And more…

Cons

  • Some modules are more useful than 1 or 2 other modules.
  • You cannot download the software to your computer or on a desktop.
  • No more cons I have found for this software.

Design Beast OTOs/Upgrades

Here are the details of its upgrade, so that you can utilize all its advanced features. In this DesignBeast Review, I have mentioned the name and price of OTOs, and the rest of the details will be available soon.

Front End: DesignBeast Commercial

Price – $47 Onetime

  • Six Designs App For Price of One
  • Mockup Designer App
  • AI Logo Maker App
  • 1-Click Background Removal App
  • Live Motion Photos App
  • Multi-Purpose Image Editor App
  • Magic Object Removal App
  • 7000+ Ready-to-Use Templates
  • Millions of Royalty-Free Images
  • Copyright-Free Vectors & Icons
  • Hundreds of Fonts
  • Multi-Lingual Support
  • Step-by-Step Video Training
  • Commercial License
  • Sell The Designs For Profit
  • Facebook Group Access
  • Skype Mentorship Group Access
  • 8 Week Training Webinars

OTO#1: DesignBeast Elite

Price – $49 Onetime

Get access to additional features worth thousands. 10X your results, sales and profits and get ahead of the competition and other DesignBeast customers. 

  • Unlock 2,000 additional ready-to-use templates
  • Get 80 new templates added to your account each month for 1 year. (no monthly or yearly fees.)
  • Thousands of Premium Text Effects and Animations
  • Millions of Premium Royalty Free Design Assets, Icons and vectors.
  • Millions of Copyright-Free Image
  • Priority Future Software Updates

OTO#2: DesignBeast Agency

Price – $67

Sell videos for $300 to $500 each with the done-for-you agency package included. This upgrade makes it easy for everyone to find clients and sell their designs for top dollar. 

  • 5 sub accounts
  • Done-For-You Agency Marketing Bundle
  • Done-For-You Legal Client Contracts
  • Done-For-You Agency Website
  • Done-For-You Agency Sales Video

OTO#3: DesignBeast 4 in 1 Ultra.

Price – $39 OneTime

Customers get access to FOUR additional apps as part of this upgrade. 

  • Pixel Perfect
  • Instantly turn any image, even a low quality image, into ultra HD, high quality photo that can be blown up to any size – even billboard size – without any pixelation or distortion.
  • Animated Ads Builder 

Create animated ads in all languages, shapes and sizes using hundreds of ready to use design templates. Use animated ads to promote your products, create ads for clients or sell animated designs on freelancer websites like fiverr, upwork and freelancer to maximize profits. 

  • Video Resizer

With this powerful technology you can resize any video into multiple video sizes perfectly sized for all social platforms. Turn a single video into multiple dimensions and sizes within minutes and share the video onto different platforms to drive more traffic and sales!

  • Video Survey Pro

With this powerful app you can instantly collect:

* Video Testimonials

* Live video feedback from clients about your work

* Add video surveys on your websites to collect valuable information

* Have your team record video feedback about any project 

Streamline your workflows without any confusion or relying on old and outdated methods like email and text.  

OTO#4: DesignBeast Unlimited

Price $67 OneTime

With the DesignBeast basic license, you can create unlimited designs forever with one limit of 600 credits per month on each of the six apps included. 

The limits reset each month so you can continue creating amazing designs, graphics and animations forever without any monthly fees. 

This limit is put in place to prevent abuse and ensure all our customers are getting the best value for years to come at an unbeatable price.

As part of this special unlimited upgrade, you can remove all the monthly limits and restrictions for all the cutting-edge apps and technologies included. 

Design Beast Review Conclusion

From my take, this will be a good and useful tool for you if you belong to these above-mentioned professional categories. No matter you have advanced skills or not because everything will be DFY and ready to use. And the best thing is that you can customize and edit each and every pre-made effect, design, and more thing. According to my opinion, graphics designing software is ned for every marketer and business person, but everyone cannot go for photoshop, AI, and Coral, so for making it easy and useful there will be a choice in your hand that is DesignBeast.

CHECK BONUSES & GRAB IT AT: https://bit.ly/3yhtcqi

SOURCE: https://bit.ly/3Dch4KV

Julie  Donnelly

Julie Donnelly

1602406920

JavaScript Promise: Methods Comparison

Introduction

Promises in JavaScript are used to handle asynchronous operations by keeping track of whether a certain event has happened. If that certain event has taken place, it determines what happens next. Promises return a value which is either a resolved value or a reason why it’s rejected. They can handle multiple asynchronous operations easily and they provide better error handling than callbacks and events.

Callback: A callback is a function that is passed into another function as an argument to be executed later.

Events: Events provide a dynamic interface to a WebPage and are connected to elements in the Document Object Model(DOM), for example: onclick(), onmouseover() etc.

A Promise has four states

Pending: Before the event has happened, the promise is in the pending state.

Settled: Once the event has happened it is then in the settled state.

Fulfilled: Action related to the promise has succeeded.

Rejected: Action related to the promise has failed.

#javascript #javascript-development #javascript-tutorial #promises #javascript-tips

A Beginner’s Guide To Promises In JavaScript

Welcome to my post about the JavaScript Promises. I hope it can be helpful since when we start programming it is difficult to enter the context.

Promises are one of the largest tools in the world of JavaScript that helps us to manage future situations in the flow of execution of a program.

The promises originated in the realm of functional programming, generally to handle asynchronous programming. In short, they allow us to define how data that will only be available in the future will be treated, specifying what will be done with that data later.

The promises were introduced in the standard in ES6, the truth is that they have been used for a long time since several libraries had implemented them to solve their needs in a more elegant way.

Image for post

The Promise object represents the eventual completion or failure of an asynchronous operation and its resulting value.

#programming #coding #javascript-promise #promises #javascript

The Definitive Guide on Javascript Promise.all()

Javascript Promise all() is an inbuilt function that returns the single Promise that resolves when all of the promises passed as the iterable have resolved or when an iterable contains no promises. The Promise .all() function can be useful for aggregating the results of the multiple promises. The Promise all() rejects with the reason of the first Promise that rejects or with the error caught by the first argument if that argument has caught the error inside it using try/catch/throw blocks.

Promise.all takes the Async operations to the next new level as it helps you to aggregate the group of  promises. In other words, we can say that it helps you to do concurrent operations.

Javascript Promise all example

Promises in JavaScript are one of the robust APIs that help us to do the Async operations.

Promise all() method rejects with a reason for the first Promise that rejects. There is no particular ordering in the execution of an array of Promises given.

On some computer systems, they may be executed in parallel or some sense concurrently, while on the other systems, they may be executed serially.

#javascript #javascript promise.all