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March 03, 2025 00:29
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Angular Cheat Sheet

A comprehensive cheat sheet for Angular, covering essential concepts, syntax, and commands for efficient development.

Core Concepts

Components

Definition: Reusable UI building blocks with a template (HTML), a class (TypeScript), and metadata.

Key Features:

  • Encapsulation of data, logic, and view.
  • Supports input (@Input) and output (@Output) properties for communication.
  • Lifecycle hooks for managing component behavior.

Creating a Component:

import { Component, Input, Output, EventEmitter } from '@angular/core';

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.css']
})
export class MyComponentComponent {
  @Input() data: any;
  @Output() action = new EventEmitter<any>();

  onClick() {
    this.action.emit(this.data);
  }
}

Using a Component:

<app-my-component [data]="item" (action)="handleAction($event)"></app-my-component>

Modules

Definition: Containers that group related components, directives, services, and other modules.

Key Features:

  • Organize application into functional units.
  • Define dependencies and providers.
  • Enable lazy loading for improved performance.

Creating a Module:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { MyComponentComponent } from './my-component.component';

@NgModule({
  declarations: [MyComponentComponent],
  imports: [BrowserModule],
  providers: [],
  bootstrap: [MyComponentComponent]
})
export class AppModule { }

Services

Definition: Reusable classes that encapsulate business logic, data access, or other functionalities.

Key Features:

  • Promote code reusability and maintainability.
  • Dependency injection for loose coupling.
  • Singleton pattern by default.

Creating a Service:

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

@Injectable({
  providedIn: 'root',
})
export class MyService {
  getData() {
    return ['item1', 'item2', 'item3'];
  }
}

Using a Service:

import { Component, OnInit } from '@angular/core';
import { MyService } from './my.service';

@Component({
  selector: 'app-consumer',
  template: `<div>{{ items }}</div>`,
})
export class ConsumerComponent implements OnInit {
  items: string[] = [];
  constructor(private myService: MyService) {}

  ngOnInit() {
    this.items = this.myService.getData();
  }
}

Templates & Data Binding

Template Syntax

Interpolation:

{{ expression }} - Displays expression value in the view.

Example:
{{ title }}

Property Binding:

[property]="expression" - Sets element property to expression value.

Example:
<img [src]="imageUrl">

Event Binding:

(event)="handler" - Binds element event to a component method.

Example:
<button (click)="onClick()">Click Me</button>

Two-way Binding:

[(ngModel)]="property" - Enables two-way data binding for form elements. Requires FormsModule.

Example:
<input [(ngModel)]="name">

Directives

Structural Directives:

Modify the DOM layout by adding, removing, or replacing elements.

  • *ngIf: Conditionally includes a template.
  • *ngFor: Repeats a template for each item in a collection.
  • *ngSwitch: Conditionally displays a template based on a switch expression.

Attribute Directives:

Change the appearance or behavior of an element, component, or another directive.

  • [ngClass]: Adds or removes CSS classes.
  • [ngStyle]: Sets inline styles.
  • ngModel: Implements two-way data binding.

Example - ngIf:

<div *ngIf="isVisible">This is visible</div>

Example - ngFor:

<div *ngFor="let item of items">{{ item }}</div>

Routing & Navigation

Routing Module

Setting up the Router:

  1. Import RouterModule and define routes.
  2. Configure routes array with path and component.
  3. Add <router-outlet> in the root component template.
  4. Use routerLink directive for navigation.

Example:

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { HomeComponent } from './home/home.component';
import { AboutComponent } from './about/about.component';

const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent },
  { path: '', redirectTo: '/home', pathMatch: 'full' },
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule { }

Navigation:

<a routerLink="/home" routerLinkActive="active">Home</a>
<a routerLink="/about" routerLinkActive="active">About</a>
<router-outlet></router-outlet>

Route Parameters

Definition:

Passing data through the URL.

Usage:

Define parameters in the route configuration.
Access parameters using ActivatedRoute.

Example Route:

{ path: 'product/:id', component: ProductComponent }

Accessing Parameter:

 
import { ActivatedRoute } from '@angular/router';

constructor(private route: ActivatedRoute) {
  this.route.params.subscribe(params => {
    const id = params['id'];
  });
}

Forms

Template-Driven Forms

Overview:

  • Relies on directives like ngModel for data binding.
  • Simpler to implement for basic forms.
  • Validation is primarily done in the template.

Example:

<form #myForm="ngForm" (ngSubmit)="onSubmit(myForm)">
  <input type="text" name="name" ngModel required>
  <div *ngIf="myForm.controls['name']?.invalid && myForm.controls['name']?.touched">
    Name is required.
  </div>
  <button type="submit" [disabled]="myForm.invalid">Submit</button>
</form>

Reactive Forms

Overview:

  • Form structure defined in the component class.
  • More control over form elements and validation.
  • Suitable for complex forms and dynamic validation.

Example:

import { FormGroup, FormControl, Validators } from '@angular/forms';

export class MyComponent {
  myForm = new FormGroup({
    name: new FormControl('', Validators.required),
    email: new FormControl('', [Validators.required, Validators.email])
  });

  onSubmit() {
    console.log(this.myForm.value);
  }
}

<form [formGroup]="myForm" (ngSubmit)="onSubmit()">
  <input type="text" formControlName="name">
  <div *ngIf="myForm.controls['name']?.invalid && myForm.controls['name']?.touched">
    Name is required.
  </div>
  <input type="email" formControlName="email">
  <div *ngIf="myForm.controls['email']?.invalid && myForm.controls['email']?.touched">
    Invalid email.
  </div>
  <button type="submit" [disabled]="myForm.invalid">Submit</button>
</form>