Terms

Question 1

Serialization

Answer 1

Serializationis the process of converting a data object—a combination of code and data represented within a region of data storage—into a series of bytes that saves the state of the object in an easily transmittable form. In this serialized form, the data can be delivered to another data store (such as anin-memory computing platform), application, or some other destination.

Question 2

Abstraction

Answer 2

Abstraction is one of thekey conceptsof object-oriented programming (OOP) languages. Its main goal is to handle complexity by hiding unnecessary details from the user. That enables the user to implement more complex logic on top of the provided abstraction without understanding or even thinking about all the hidden complexity.

Question 3

Granular

Answer 3

Granular - In computer science, granularity refers toa ratio of computation to communication– and also, in the classical sense, to the breaking down of larger holistic tasks into smaller, more finely delegated tasks

Question 4

Base64

Answer 4

• encoding isthe process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized format for efficient transmission or storage.
• Encode information
• Sending binary data over texted based protocol such as HTTP
• Ensures text doesn’t get corrupted during transfer
• Doesn’t conceal data
• e.g submit HTML form using base64

Question 5

Polyfill

Answer 5

Polyfill - assists with creating code that is compatible with multiple browsers

Question 6

Compile Time

Answer 6

code that is compiled into machine code to become an executable program

Question 7

Run Time

Answer 7

compiled program that can be opened and run by user, when an application is running, this is called run time

Question 8

Static Typing

Answer 8

Static typingmeans that the executable form of a program generated at compile time will vary depending upon the types of data values found in the program

Question 9

Dynamic Typing

Answer 9

means that the generated code will always be the same irrespective of the type — any differences in execution will be determined at run time.

Question 10

Tree Shaking

Answer 10

Tree Shaking - It can happen that we add code to our bundle that isn’t used anywhere in our application. This piece ofdead codecan be eliminated in order to reduce the size of thebundle, and prevent unnecessarily loading more data! The process of eliminatingdead code before adding it to ourbundle is calledtree-shaking

Question 11

Scopes

Answer 11

Scopes are where you can talk about variables

• Lexical scope - show up in document specifically
• Relate to runtime
• Region of code
• This keyword
• this is a input parameter that refers to the left of the dot at calltime
• this is an input parameter between the parentheses (function invocation) that gets its name assigned and talks about the object to the left of the dot at callltime. So you don’t have to pass parameters

Question 12

Heuristic Programming

Answer 12

employs a practical method, not guaranteed to be optimal, perfect, logical, or rational, but instead sufficient for reaching an immediate goal

Question 13

SSH

Answer 13

SSH, also known as Secure Shell or Secure Socket Shell, is a network protocol that gives users, particularly system administrators, a secure way to access a computer over an unsecured network.

Question 14

HTTP

Answer 14

• Protocol for communication between web servers and clients
• Every request is completely stateless (doesn’t remember the requests)
• HTTPS is Hyper text transfer protocol secure
• Data sent is encrypted (SSL / TLS)

Question 15

Node

Answer 15

• comes with many APIs suitable for backened development e.g filesystems http requests, streams, child processes
• efficient with real time applications and facilitates multiple client requests, enables resharing and resuing packages of library code

Question 16

How node works

Answer 16

• event-driven, server consists of one thread processing event one after another
• server doesn’t wait for process to complete but registers callback function
• server needs to create additional threads or switch between threads
• Single threaded event loop model

Question 17

Authentication vs Authorization

Answer 17

• authentication is process of verifying identity of user by obtaining credentials and verifying user
• if credentials are valid, authorization process starts
• authentication -> authorization
• authorization is process of allowing authenticated users to access resources

Question 18

Middleware

Answer 18

• refers to reusable components plugged into express application
• consists of functions that handle HTTP requests
• manipulates request and response objects and sends response to client or pass control to following middleware
• app.use() for express middleware
• calling next() moves onto next middleware or route

Question 19

Stream

Answer 19

• sequence of data being moved from one point to another over time
• don’t need to wait for all data to be available before processing when huge amount of data to process
• big data is broken down and sent in chunks

Question 20

JWT

Answer 20

• explicit, compact self contained secured protocol
• digitally signed and encrypted
• stateless, all information needed to complete a particular request is sent along with it including an Authorization HTTP header
• JWT are signed and contents are protected from tampering, can’t change contents without invalidating them

Question 21

Long Polling

Answer 21

• Instead of resolving request immediately with result, have server hold onto request until server has data available
  
  • Creates open connection with server
  • Solves latency problem from polling
  • Cons - Maintain open connection, still have to initiate new request to get new data from server

Question 22

WebSocket

Answer 22

• Maintain open connection, duplex connection
  
  • TCP protocol (16 bits for port number) limit of 65k connections per server
  • Needs lots of server to handle multiple web socket connections
  • Use load balancer to many requests

Question 23

DOM

Answer 23

• document object model, an API for webpage allows program to read and manipulate page content structure and styles
• DOM is object-based representation of source HTML document
• converts structure/content of HTML document into object model used by various programs
• Represented by a node tree

Question 24

Redis

Answer 24

Redis
- noSQL database
- alll data stored as key value pairs
- one giant JSON object
- not good at storing structured data
- good at storing individual key value pairs
- incredibly fast runs inside of working memory (RAM)
- more volatile , system crashes you lose everything in REDIS
- generally not used as persisent database
- used more for caching
- things that take longer to compute usually stored in REDIS
- built on top of traditional DB, sits in front traditional DB
- used for long, slow queries or data that is accessed frequentyl but doesn’t change
- store this information in redis and database and if it’s in redis, query will be much faster 100 to 1000 times faster
- redis stores values as string by default

Question 25

Singleton JS Pattern

Answer 25

Singleton - Single global instance that is shared throughout application. Allows us to use a single instance across multiple files without having to reinstantiate it across multiple files.
Freeze the class/object so that the object is not modifiable

Pros: Potentially save lots of memory
Cons: ES2016 Modules are singletons by default

Question 26

Proxy JS Pattern

Answer 26

Proxy - is used to intercept requests to a targeted object and decide whether or not to forward on those requests. Proxies make it easy to add functionality such as validation, logging, formatting, notifications, and debugging.

Pros: add functionality to a project, add validation
Cons: Methods run every time run-ing proxy object which can lead to performance issues

Question 27

Observe Pattern

Answer 27

Observe Pattern - consists of an observable object and subscribers that will be notified by the observable object. This creates an efficient separation of concerns because the observable object has no knowledge of the subscribers. The subscribers are not aware of the underlying implementation that leads to the notification.

Question 28

Factory Pattern

Answer 28

Factory Pattern - is a function that returns an object. The function may accept parameters and use those parameters to create more properties on the returned object. This pattern is useful when creating multiple objects that share the same set of properties.

Question 29

Prototype Pattern

Answer 29

Prototype Pattern - which is more memory efficient than the factory pattern because it avoids the duplication of shared properties and methods by elevating them up the prototype chain. The prototype pattern can be used with the Object.create method or with ES6 classes.

Question 30

Monolith Architecture

Answer 30

Monolith
- Misconception that monolith are huge machine that runs entire service
- Doens’t have to be single, might be multiple monolith service

PROS
- Good for small teams
- Less Complexity
- Less Duplication (less pipelines)
- Procedure calls are faster because calling same instance
CONS
- More context required for new members
- Complicated Deployments (monitored after every deployment and not decoupled)
- Much more responsibility on each server (single point of failure)

Question 31

Microservices

Answer 31

• Misconception that micro service ne function running on one machine with tiny databases that are interconnected
• Clients are connected to different microservices
• Separate services based on concern of service
• Usually talk to own dedicated micro services
  PROS
• Easier to scale, only caring about its own data
• Easier to design
• Easy for onboarding new team, only understand context of feature they’re working on
• Working in parallel, can work on multiple features at one time
  CONS
• Needs skilled architect
• Might need to justify microservice architecture

Question 32

Virtualization

Answer 32

Virtualization has its roots at the beginning of computer science when large, expensive mainframe computers were the norm. How could multiple programmers use the same single machine? The answer was virtualization and specifically virtual machines which are complete copies of a computer system from the operating system on up.

Question 33

Docker

Answer 33

Docker is a way to isolate an entire operating system via Linux containers which are a type of virtualization

• Virtualization software that makes developing and deploying applications much easier
• Packages application with necessary dependencies, configuration, system tools and runtime
• Standardized unit that has everything the application needs to run

Question 34

Virtual Machine vs Docker

Answer 34

• OS has 2 main layers (OS Kernel and OS Application Layer)
• OS Kernel is what communicates with hardware components (CPU, memory storage)
• Kernel is the core of every operation system and interacts between hardware and software components
• Docker virtualizes the applications layer
• It contains the OS application layer and services and apps installed on top of that layer (e.g Java runtime)
• Main difference is that VM virtualizes both Kernel and Applications layer
• When you download VM image on your host, it boots up its own Host

Question 35

Difference between Docker and Virtual Machine

Answer 35

• Docker images are much smaller because it only implements one layer of OS
  
  • Docker images are couple of MB , VM images are couple of GB
  • Docker containers take seconds to start as it reuses the host kernel, VMs take minutes to start
  • Virtual machines compatible with all OS, Docker is not compatible with Linux Distros
  • Linux based Docker images cannot use Windows kernel
  • Most containers are linux based, originally built for linux
  • Docker Desktop allows you to run Linux containers on Mac and Windows
  • Docker Desktop uses a hypervisor layer with lightweight linux distro

Question 36

Encapsulation

Answer 36

Encapsulation is the mechanism of binding the data together and hiding it from the outside world. Encapsulation is achieved when each object keeps its state private so that other objects don’t have direct access to its state. Instead, they can access this state only through a set of public functions.

Question 37

Abstraction

Answer 37

Abstraction: Abstraction can be thought of as the natural extension of encapsulation. It means hiding all but the relevant data about an object in order to reduce the complexity of the system. In a large system, objects talk to each other, which makes it difficult to maintain a large code base; abstraction helps by hiding internal implementation details of objects and only revealing operations that are relevant to other objects.

Question 38

Inheritance

Answer 38

Inheritance: Inheritance is the mechanism of creating new classes from existing ones

Question 39

Polymorphism

Answer 39

Polymorphism (from Greek, meaning “many forms”) is the ability of an object to take different forms and thus, depending upon the context, to respond to the same message in different ways. Take the example of a chess game; a chess piece can take many forms, like bishop, castle, or knight and all these pieces will respond differently to the ‘move’ message.