import 'rxjs/add/operator/map';

import { map } from 'rxjs/operators';

import { map, catchError, tap } from 'rxjs/operators';

import { Observable } from 'rxjs/Rx';

import { Observable } from 'rxjs/Observable';

import 'rxjs/add/observable/throw';

Observable.throw('error');

import { ErrorObservable } from 'rxjs/observable/ErrorObservable';

ErrorObservable.create('error');

import "rxjs/add/observable/timer";

const timerSource$ = Observable.timer(initialDelay);

import { timer } from 'rxjs/observable/timer';  

const timerSource$ = timer(initialDelay);

import { from} from 'rxjs/observable/from';
import { map, scan, filter } from 'rxjs/operators';

const source$ = range(1,10);

const sumOfSquaredOddNumbers$ = source$.pipe(
   filter(n => n % 2 !== 0), 
   map(n => n * n),
   scan((acc,s) => acc + s, 0)
);
sumOfSquaredOddNumbers$.subscribe(v => console.log(v));

/*** Output ****/ 
1
10
35
84
165

import { of } from 'rxjs/observable/of';
import { from } from 'rxjs/observable/from';
import { range } from 'rxjs/observable/range';

const source$ = of(1,2,3);
const rangeSource$ = range(0,5);

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/filter';

names = allUserData.
         map(user => user.name).
         filter(name => name);

import { Observable } from 'rxjs/Observable';
import { map, filter } from 'rxjs/operators';

names = allUserData.pipe(
   map(user => user.name),
   filter(name => name),
);

npm install -g @angular/cli

 ng new my-math-app

 ng generate library ts-math-example

export function add(num1: number, num2: number) {
    return num1 + num2;
}

/*
* Public API Surface of ts-math-example
*/
export * from './lib/math';

ng build ts-math-example --prod
cd dist/ts-math-example
npm publish

 import { add } from '@myuser/ts-math-example';

  var manager = new breeze.EntityManager({  
  dataService: dataService,          
  metadataStore: metadataStore,                     
  saveOptions: new breeze.SaveOptions({    allowConcurrentSaves: true, tag: [{}] })   
                 });

var dataService = new breeze.DataService({  
serviceName: "/breeze/"+ "Automobile",             
hasServerMetadata: false,
namingConvention: breeze.NamingConvention.camelCase        
});
var metadataStore = new breeze.MetadataStore({});

[BreezeController]
public class AutomobileController : ApiController
    {
        readonly EFContextProvider<ApplicationDbContext> _contextProvider =
        new EFContextProvider<ApplicationDbContext>();
        [HttpGet]
        public string Metadata()
        {
            return _contextProvider.Metadata();
        }
        [HttpGet]
        public IQueryable<Customer> Customers() {
           return _contextProvider.Context.Customers;
        }

        [System.Web.Http.HttpPost]
        public SaveResult SaveChanges(JObject saveBundle)
        {
           _contextProvider.BeforeSaveEntitiesDelegate = BeforeSaveEntities;
           _contextProvider.AfterSaveEntitiesDelegate = afterSaveEntities;
            return _contextProvider.SaveChanges(saveBundle);
        }
protected Dictionary<Type, List<EntityInfo>> BeforeSaveEntities(Dictionary<Type, List<EntityInfo>> saveMap)
        {
        }
private void afterSaveEntities(Dictionary<Type, List<EntityInfo>> saveMap, List<KeyMapping> keyMappings)
        {
        }
    }

This is a guide that everyone can use to learn about the practice of front-end development. It broadly outlines and discusses the practice of front-end engineering: how to learn it and what tools are used when practicing it in 2019. 

  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.0.0" PrivateAssets="All" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.0.0" PrivateAssets="All" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="2.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.0.0" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0" />
  </ItemGroup>

Unable to create an object of type 'ApplicationDbContext'. 
Add an implementation of 'IDesignTimeDbContextFactory<ApplicationDbContext>' to the project, 
or see https://go.microsoft.com/fwlink/?linkid=851728 for additional patterns supported at design time.

    public class ApplicationDbContextFactory : IDesignTimeDbContextFactory<ApplicationDbContext>
    {
        public ApplicationDbContext CreateDbContext(string[] args)
        {
            return new ApplicationDbContext(siteSettings, httpContextAccessor, hostingEnvironment, logger);
        }
    }

public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<MyDbContext> 
{ 
    public MyDbContext CreateDbContext(string[] args) 
    { 
        IConfigurationRoot configuration = new ConfigurationBuilder() 
            .SetBasePath(Directory.GetCurrentDirectory()) 
            .AddJsonFile("appsettings.json") 
            .Build(); 
        var builder = new DbContextOptionsBuilder<MyDbContext>(); 
        var connectionString = configuration.GetConnectionString("DefaultConnection"); 
        builder.UseSqlServer(connectionString); 
        return new MyDbContext(builder.Options); 
    } 
}

How to build and publish an Angular module 

Based on the above observations, we can conclude that React will be the best framework to learn in 2021, followed by Vue. But there is a high chance of Angular defending second place since it has been there for a longer period of time than Vue, and surely 2021 is not the end of that. So if you are an Angular developer, I suggest you learn React in the upcoming days.