Class/Record/Struct

 

Feature	Class	Record	Struct
Type	Reference Type	Reference Type (since C# 10, can be record struct)	Value Type
Memory Allocation	Typically allocated on the heap.	Typically allocated on the heap.	Typically allocated on the stack (or heap if used as part of a class or array)
Default Constructor	Can have a parameterless constructor, and can be explicitly defined.	Implicit parameterless constructor is not allowed; parameters are required.	Parameterless constructor is provided by default and initializes all fields to default values.
Inheritance	Supports inheritance (can inherit from other classes and be inherited).	Supports inheritance (can inherit from other records but not from classes).	Does not support inheritance (cannot inherit from or be inherited by other types).
Equality	Uses reference equality by default, can override Equals and GetHashCode for value-based equality.	Uses value-based equality by default (based on all properties). Automatically implements Equals, GetHashCode, and ToString.	Uses value-based equality by default (based on all fields). Automatically implements Equals, GetHashCode, and ToString.
Mutability	Mutable by default; properties can be changed after object creation.	Immutable by default; properties are readonly and set via constructor.	Immutable by default (properties are typically readonly and initialized in the constructor).
Deconstruction	Not supported by default.	Supports deconstruction with tuple-like syntax.	Supports deconstruction with tuple-like syntax.
Constructor	Can have multiple constructors with various parameters.	Primary constructor is defined with positional parameters; can also have additional constructors.	Constructor must initialize all fields; no parameterless constructor allowed unless provided by the compiler.
Default Values	Fields initialized to default values if not explicitly set.	Properties are initialized via the constructor.	Fields are initialized to default values (e.g., 0, null).
Use Cases	Used for complex objects with behavior and mutable state.	Ideal for immutable data models, DTOs, and scenarios where value-based equality is important.	Ideal for lightweight, immutable data structures where copying and stack allocation are beneficial.

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Angular Basics

Intro

•    package.json

•     (list of dependencies)

•    package-lock.json

•     (details list of that dependencies)

•    angular.json

•     (map everything here: assets, scripts etc)

•    tsconfig.json

•     (typescript configuration file)

•    polyfills.ts

•     (compatibility file)

 

Components

•    Modules must be declared in the imports

•    Components must be declared in the declarations

•    Standalone components are not dependent in any modules and it must be declared in imports

•    and Pipes are doing the transformation over text

Bindings - Two Way, Property, Event

Routing

•    Basic Routing

•      Routes – for mapping path & component

•      routerLink – navigate to different routes

•      router-outlet– for displaying matched route

•    Child routing

•     Activated Route (const routeId = route.snapshot.paramMap.get(‘id’);)

•    Module Routing

•     const routes : Routes

•    Lazy Loading

•     Load when required (loadChildren then import)

Directives

•    Add additional behavior to elements

•    Components works as a directive

•    Attribute Directive

ngClass (Binding Classes)

ngStyle (Binding Styles, Only accept objects s = {})

ngModel (Two Way Binding)

•    Structural Directive

*ngIf

*ngFor

*ngSwitch

Services

•    Defined with @Injectable

•    All are in observable format and without subscribe it won’t work (Rxjs feature)

FormType

•    TDF – handle in html file

•     ngForm

•    Reactive – handle in ts file

•     FormGroup

Guard

•    used to control access in particular route

•    canActivate

•    canActivateChild

•    canDeactivate

•    canLoad

Interceptor

•    Used for token login

•    Declares in app.module [Providers]

Rxjs

•    Observable and Operators

•    Promise (then, then, finally)    

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Reactive Programming

🔎Definition---

JavaScript Promises are objects used to represent the eventual completion (or failure) of an asynchronous operation. They are widely used in modern JavaScript to handle asynchronous tasks in a more readable and manageable way, compared to traditional callback-based approaches. A Promise can be in one of three states:
Pending: Initial state, neither fulfilled nor rejected.
Fulfilled: The operation completed successfully.
Rejected: The operation failed.

On the other hand, RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using observables. An observable represents a stream of data that can be observed over time. It provides powerful tools for handling asynchronous and event-based programming.

🔩Conversion---

Converting a Promise to an Observable is a common operation in RxJS when integrating with libraries or APIs that return Promises. RxJS provides the from function to convert various data sources, including Promises, into Observables.

Converting an Observable to a Promise is useful when you need to work with Promise-based APIs or when you want to consume Observables in a Promise-based context. RxJS provides the toPromise() operator to convert an Observable into a Promise.

🔚Conclusion---

Promises are simpler and more straightforward for handling single asynchronous operations that produce a single value or error.

Observables are more powerful and suitable for handling multiple asynchronous values over time, supporting cancellation, and offering a wide range of operators for transforming and combining streams of data. When you promise you can't cancel and for cancelling you have to use another library. But you can Unsubscribe to cancel in observables. Also you have to unsubscribe every time that means writing same code couple of times when working on a  big project but in Promises it will go on rejected state.

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Run React Globally

 If you have problems running create-react-app in text editors but the package is installed globally. So here is the SOLUTION-------------

1. Open PowerShell as an administrator. You can do this by right-clicking on the Windows Start button and selecting "Windows PowerShell (Admin)".

2. In the PowerShell window, run the following command to check the current execution policy:

   powershell
   Get-ExecutionPolicy
   

3. The output will be one of the following:

   • Restricted: This means that script execution is disabled. You need to change it to a more permissive policy.
   • AllSigned or RemoteSigned: These policies allow script execution but require digitally signed scripts. If you encounter this, you can skip changing the execution policy and try using the npx create-react-app command instead of create-react-app.

4. To change the execution policy to allow script execution, run the following command:

   powershell
   Set-ExecutionPolicy Unrestricted
   

5. You will be prompted to confirm the change. Type Y and press Enter.

6. After changing the execution policy, you should be able to use the create-react-app command without encountering the "running scripts is disabled" error.

7. Once you've finished using create-react-app, it's recommended to set the execution policy back to a more secure value. Run the following command:

   powershell
   Set-ExecutionPolicy Restricted
   

By following these steps, you should be able to resolve the script execution error and use create-react-app globally in any text editor.

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