Node js interview questions

This blog is just for revision .

• Explain the version of a package in node js 

1. major
2. minor
3. patch
4. pre major
5. pre minor
6. pre patch
7. pre release

• What is the use of ~ and ^

1. ~ matches the most recent patch version for the minor version
2.  ^ matches the most recent minor version of the major version     

• What are modules

Modules are way of organising reusable components

1. Core
2. Local
3. Third party

• What is the use of require()

It is used to import core modules.It is a function that can be used to import symbols from another module to the current scope

• What is commonjs

Commonjs defines standards for modules, packages and unit testing.

• What is AMD ?

Asynchronous

• Explain the parts of package.json

1. name
2. version
3. license
4. description

• Explain async functions
• Explain await

mat-form-field must contain a MatFormFieldControl.

Hi Guys ,

Today I have faced this error :

ERROR Error: mat-form-field must contain a MatFormFieldControl.

Later I have found out that I have missed to add the attribute matInput .

<mat-form-field>

<input type="text" name="name" ngModel #refName="ngModel" name="name" required >

</mat-form-field>

Once I added the attribute to the input field matInput , the error was resolved .

<mat-form-field>

<input matInput type="text" name="name" ngModel #refName="ngModel" name="name" required >

</mat-form-field>

Video Link :

Full stack trace is as below .

CustDetailComponent.html:4 ERROR Error: mat-form-field must contain a MatFormFieldControl.
    at getMatFormFieldMissingControlError (form-field.es5.js:119)
    at MatFormField.push../node_modules/@angular/material/esm5/form-field.es5.js.MatFormField._validateControlChild (form-field.es5.js:771)
    at MatFormField.push../node_modules/@angular/material/esm5/form-field.es5.js.MatFormField.ngAfterContentInit (form-field.es5.js:453)
    at callProviderLifecycles (core.js:9553)
    at callElementProvidersLifecycles (core.js:9534)
    at callLifecycleHooksChildrenFirst (core.js:9524)
    at checkAndUpdateView (core.js:10455)
    at callViewAction (core.js:10692)
    at execComponentViewsAction (core.js:10634)
    at checkAndUpdateView (core.js:10457)

oracle plsql interview questions

Important Oracle PL SQL interview Questions .

•  What is oracle database ?

 A database is a set of physical files on disk created by the CREATE DATABASE statement .

• What is a database instance ?

A database instance is a set of memory structures that manage database files

What is a record type.
Group of related data items stored in fields.

What is a collection type
Ordered group of elements all of same type


What is type ref cursor
Data type whose value is in memory address of query work area of the database

• What is an index ?

By creating an index on one or more columns of a table, you gain the ability in some cases to retrieve a small set of randomly distributed rows from the table .

• What are triggers ?

triggers are procedures stored in PL/SQL or Java that run (fire) implicitly whenever a table or view is modified or when some user actions or database system actions occur.

1. DML
2. DDL

• Implicit attributes of Cursor

1. %FOUND
2. %ISOPEN
3. %NOTFOUND
4. %ROWCOUNT

• What is a DB Link ?

it is a schema object in one database that enables you to access objects on another database .

•  What is a cluster ?

 A cluster is a schema object that contains data from one or more tables, all of which have one or more columns in common

• What is a tablespace? 

it is an allocation of space in the database that can contain schema objects.

Types of tablespace .

1. A permanent tablespace contains persistent schema objects. Objects in permanent tablespaces are stored in datafiles.
2. An undo tablespace is a type of permanent tablespace used by Oracle Database to manage undo data if you are running your database in automatic undo management mode. Oracle strongly recommends that you use automatic undo management mode rather than using rollback segments for undo.
3. A temporary tablespace contains schema objects only for the duration of a session. Objects in temporary tablespaces are stored in tempfiles.

• What is SQL*Plus ?

SQL*Plus has a command-line user interface that acts as the client when connecting to the database.

• What is sql loader ?

SQL*Loader is a bulk loader utility used for moving data from external files into the Oracle database.

• Explain normalization.

Normalization is a process of organizing the data in database to avoid data redundancy, insertion anomaly, update anomaly & deletion anomaly.

Terminology :

1. attribute : column

2. candidate key : primary key ( simple or composite )

3. prime attribute : column which is part of primary key

4. non prime attribute : column not part of primary key .

5. super key : any set of attributes which identifies a unique record .

6. functional dependency : B depends on A 

7. transitive dependency : B is dependent of A . C is dependent of B . So C has a transitive dependency on A .

1NF : attribute should be atomic.

2NF : non prime attribute should not depend on a subset of primary key

3NF : non prime attribute should not have transitive dependency with the super key .

BCNF : any functional dependency should be a super key .

Angular Quiz

Score :

0

Test your understanding

angular-cli.json was deprecated in which version ?

v5

v4

v6

v7

Info

Next

core.js:1673 ERROR Error: Uncaught (in promise): TypeError: instance[output.propName].subscribe is not a function

Hi Guys ,

Today I have faced this error :

core.js:1673 ERROR Error: Uncaught (in promise): TypeError: instance[output.propName].subscribe is not a function

Later I have found out that I have imported the EventEmitter from a different package in my component file :

import { EventEmitter } from 'events';

Later when I changed the package to @angular/core it worked fine .

import { EventEmitter } from '@angular/core';

The full stack trace is below for your reference :

ERROR Error: Uncaught (in promise): TypeError: instance[output.propName].subscribe is not a function
TypeError: instance[output.propName].subscribe is not a function
    at createDirectiveInstance (core.js:9183)
    at createViewNodes (core.js:10399)
    at callViewAction (core.js:10715)
    at execComponentViewsAction (core.js:10634)
    at createViewNodes (core.js:10427)
    at createRootView (core.js:10313)
    at callWithDebugContext (core.js:11344)
    at Object.debugCreateRootView [as createRootView] (core.js:10831)
    at ComponentFactory_.push../node_modules/@angular/core/fesm5/core.js.ComponentFactory_.create (core.js:8659)
    at ComponentFactoryBoundToModule.push../node_modules/@angular/core/fesm5/core.js.ComponentFactoryBoundToModule.create (core.js:3311)
    at resolvePromise (zone.js:831)
    at resolvePromise (zone.js:788)
    at zone.js:892
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:423)
    at Object.onInvokeTask (core.js:3811)
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:422)
    at Zone.push../node_modules/zone.js/dist/zone.js.Zone.runTask (zone.js:195)
    at drainMicroTaskQueue (zone.js:601)
defaultErrorLogger @ core.js:1673
push../node_modules/@angular/core/fesm5/core.js.ErrorHandler.handleError @ core.js:1719
next @ core.js:4311
schedulerFn @ core.js:3551
push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.__tryOrUnsub @ Subscriber.js:196
push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.next @ Subscriber.js:134
push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._next @ Subscriber.js:77
push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next @ Subscriber.js:54
push../node_modules/rxjs/_esm5/internal/Subject.js.Subject.next @ Subject.js:47
push../node_modules/@angular/core/fesm5/core.js.EventEmitter.emit @ core.js:3535
(anonymous) @ core.js:3842
push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @ zone.js:391
push../node_modules/zone.js/dist/zone.js.Zone.run @ zone.js:150
push../node_modules/@angular/core/fesm5/core.js.NgZone.runOutsideAngular @ core.js:3779
onHandleError @ core.js:3842
push../node_modules/zone.js/dist/zone.js.ZoneDelegate.handleError @ zone.js:395
push../node_modules/zone.js/dist/zone.js.Zone.runGuarded @ zone.js:164
_loop_1 @ zone.js:694
api.microtaskDrainDone @ zone.js:703
drainMicroTaskQueue @ zone.js:608
Promise.then (async)
scheduleMicroTask @ zone.js:584
push../node_modules/zone.js/dist/zone.js.ZoneDelegate.scheduleTask @ zone.js:413
push../node_modules/zone.js/dist/zone.js.Zone.scheduleTask @ zone.js:238
push../node_modules/zone.js/dist/zone.js.Zone.scheduleMicroTask @ zone.js:258
scheduleResolveOrReject @ zone.js:879
ZoneAwarePromise.then @ zone.js:1012
push../node_modules/@angular/core/fesm5/core.js.PlatformRef.bootstrapModule @ core.js:4345
./src/main.ts @ main.ts:11
__webpack_require__ @ bootstrap:76
0 @ main.ts:12
__webpack_require__ @ bootstrap:76
checkDeferredModules @ bootstrap:43
webpackJsonpCallback @ bootstrap:30
(anonymous) @ main.js:1

ERROR Error: Uncaught (in promise): Error: Cannot match any routes.

Hi Guys ,

Today I have faced this error :

ERROR Error: Uncaught (in promise): Error: Cannot match any routes. 

We will face this error when we enter the URL of the angular app and the URL does not have a matching route configured . To verify that check your AppModule or AppRoutingModule . 

1. check the router array :

const appRoutes:Routes =[

{path:'cust-detail',component: CustDetailComponent},

{path:'mcq',component: MCQComponent},

{path:'sign-up',component: SignUpComponent}

];

if the path is missing add to it .

2. check the import array :

imports: [

BrowserModule,

  FormsModule,

  ReactiveFormsModule,

  RouterModule.forRoot(appRoutes),

],

You need to have the RouterModule.forRoot(appRoutes) present in your application.

The full stack trace is below for your reference :


ERROR Error: Uncaught (in promise): Error: Cannot match any routes. URL Segment: 'test'
Error: Cannot match any routes. URL Segment: 'test'
    at ApplyRedirects.push../node_modules/@angular/router/fesm5/router.js.ApplyRedirects.noMatchError (router.js:1384)
    at CatchSubscriber.selector (router.js:1365)
    at CatchSubscriber.push../node_modules/rxjs/_esm5/internal/operators/catchError.js.CatchSubscriber.error (catchError.js:34)
    at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._error (Subscriber.js:80)
    at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.error (Subscriber.js:60)
    at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._error (Subscriber.js:80)
    at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.error (Subscriber.js:60)
    at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._error (Subscriber.js:80)
    at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.error (Subscriber.js:60)
    at TapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/tap.js.TapSubscriber._error (tap.js:61)
    at resolvePromise (zone.js:831)
    at resolvePromise (zone.js:788)
    at zone.js:892
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:423)
    at Object.onInvokeTask (core.js:3811)
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:422)
    at Zone.push../node_modules/zone.js/dist/zone.js.Zone.runTask (zone.js:195)
    at drainMicroTaskQueue (zone.js:601)

Web services Interview Questions

Web Services Interview Questions.
This blog is just for revision.

• What is SOAP Web Services

SOAP ( simple object access protocol) based web services (application exchange information over network)  .

• What is Contract first ?

WSDL or XSD is created first , then the java classes .

• What is WSDL ?

WS Description Language , it describes a web service .

• What are the parts of wsdl ?

1. types : data types used 
2. message : request and response
3. portType : operations available
4. binding : 
5. Operations:
6. Service :

Types

Schema

Contract namespace

Schema location xsd

Message can be multiple

Part

Name

Element

Type


Port type
Operation
Input, output,fault



Binding
Style document/ RPC transport
Operation
Input
Header, body
Output
Header,body
Fault
Fault

Service
Port
Binding
Location

• What is XSD ?

It defines schema which defines structure of xml.

• Explain wsdl2java

Use pluggin cfx-codegen-pluggin
Goal wsdl2java
Wsdl location
Binding files
Note : wsdl will have xsd,a java class for each xsd will be generated.

• What are the elements of soap message?

1. Envelope
2. Header
3. Body
4. Fault

•  What are SOLID principles in Rest Web services Development ?

1. Single Responsibility : Each class has only one function 
2. Open for Extension Closed for Modification : existing classes should not be modified , instead new classes should be created .
3. Liskov Substitution Principle :  App should work fine if we substitute subclass in place of super class .
4. Interface Segregation : large interfaces should be divided into smaller ones .
5. Dependency Inversion : loose coupling .