Common places and scenarios where new keyword is used in Angular projects

 In Angular, the new keyword is used to create instances of classes. While Angular primarily relies on Dependency Injection (DI) for services and components, you may explicitly use new in specific scenarios. Below is a categorized list of common use cases:

Common Use of new in Angular

Where it's used	Example	Explanation
Creating a class instance	let person = new Person();	Standard JavaScript usage in services or components
Creating Dates	let now = new Date();	Frequently used in date pickers or logging
Creating FormGroups	new FormGroup({...})	Reactive Forms: defining a new form group
Creating FormControls	new FormControl('value')	Reactive Forms: defining individual form controls
Custom Error Classes	throw new CustomError('Something went wrong');	Angular apps often define custom error classes
HttpHeaders or HttpParams	new HttpHeaders().set('Authorization', 'Bearer')	Used to configure HTTP requests
Creating Observables	new Observable(observer => {...})	Sometimes used to create custom observables
Using new in RxJS operators	new Subject() or new BehaviorSubject()	Common in services or state management
Dependency Injection (rare)	new SomeService() (not recommended)	Not recommended; use Angular DI instead

🔸 Angular-Specific Classes Often Instantiated with new

These are common classes you might instantiate with new:

• FormControl

• FormGroup

• FormArray

• HttpHeaders

• HttpParams

• DatePipe, CurrencyPipe, etc. (though usually injected, sometimes instantiated manually)

• BehaviorSubject, Subject, ReplaySubject (from RxJS)

• Custom model classes (e.g., new UserModel())

• Custom error classes

✅  Common Angular Classes You Instantiate with new

These are safe and common classes that you can instantiate with new in your Angular application:

🔹 Frequently Used with new

📦 Forms (@angular/forms)

• FormControl

• FormGroup

• FormArray

const name = new FormControl('John');
const form = new FormGroup({ name: name });

🌐 HTTP (@angular/common/http)

• HttpHeaders

• HttpParams

const headers = new HttpHeaders().set('Authorization', 'Bearer token');

📊 RxJS

• Subject

• BehaviorSubject

• ReplaySubject

const subject = new BehaviorSubject<number>(0);

📆 Date & Utilities

• Date

• Custom class instances

const date = new Date();
const user = new UserModel();

❗ Error Classes

• HttpErrorResponse (sometimes)

• Custom error classes

• -n shows line numbers

• -w matches the whole word

 Internal Usages (some examples)

Module/Area	Used with new	Purpose
@angular/forms	new FormControl(), new FormGroup()	Used in reactive forms
@angular/common/http	new HttpHeaders(), new HttpParams()	Used to configure HTTP requests
@angular/core/testing	new TestBed() (indirectly)	Internally during unit testing
RxJS (used in Angular)	new Subject(), new BehaviorSubject()	Angular uses these for observable patterns