What is the difference between template-driven and reactive forms?

In Angular, both template-driven and reactive forms are used to handle form input and validation—but they differ in approach, control, and structure.

Here’s a clear breakdown of the differences between template-driven and reactive forms:

What is the difference between template-driven and reactive forms?

🧾 1. Form Structure

Feature	Template-Driven Form	Reactive Form
Code Location	Logic is mainly in the HTML template	Logic is mainly in the TypeScript code
Form Definition	Uses Angular directives (`ngModel`)	Uses `FormControl`, `FormGroup`, `FormBuilder`
Control	Angular controls the form	Developer has explicit control

💻 2. Setup & Syntax Example

Template-Driven (HTML-Heavy):

<form #f="ngForm">
  <input name="username" [(ngModel)]="user.name" required>
</form>

Reactive (TS-Heavy):

form = new FormGroup({
  username: new FormControl('', Validators.required)
});

<form [formGroup]="form">
  <input formControlName="username">
</form>

🔍 3. Validation

Feature	Template-Driven	Reactive
Style	Declarative (in HTML)	Programmatic (in TypeScript)
Custom Validators	Less flexible	Very flexible and testable
Async Validation	Not ideal	Easily implemented

⚙️ 4. Use Cases

✅ Template-Driven:
- Simple forms
- Small projects
- Forms that don’t need complex logic
✅ Reactive:
- Large/complex forms
- Dynamic form fields
- Complex validation and unit testing needs

🎯 Summary

Aspect	Template-Driven	Reactive
Control Level	Less	More
Scalability	Limited	High
Code Complexity	Simpler (HTML-heavy)	More structured (TS-heavy)
Testing	Harder	Easier

Explain the Angular compilation process: View Engine vs. Ivy.

The Angular compilation process transforms your Angular templates and components into efficient JavaScript code that the browser can execute. Over time, Angular has evolved from the View Engine compiler to a newer, more efficient system called Ivy . Here's a breakdown of the differences between View Engine and Ivy , and how each affects the compilation process: 🔧 1. What Is Angular Compilation? Angular templates ( HTML inside components) are not regular HTML—they include Angular-specific syntax like *ngIf , {{ }} interpolation, and custom directives. The compiler translates these templates into JavaScript instructions that render and update the DOM. Angular uses Ahead-of-Time (AOT) or Just-in-Time (JIT) compilation modes: JIT : Compiles in the browser at runtime (used in development). AOT : Compiles at build time into efficient JS (used in production). 🧱 2. View Engine (Legacy Compiler) ➤ Used in Angular versions < 9 🔍 How It Works: Compiles templat...

What are the different types of directives in Angular? Give real-world examples.

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Explain the concept of ControlValueAccessor in custom form components.

In Angular, the ControlValueAccessor interface is what allows custom form components to work seamlessly with Angular forms (both reactive and template-driven). 🧠 What is ControlValueAccessor ? It’s an Angular bridge between your custom component and the Angular Forms API . When you use a custom form component (like a date picker, dropdown, slider, etc.), Angular doesn't automatically know how to read or write its value. That’s where ControlValueAccessor comes in. It tells Angular: How to write a value to the component How to notify Angular when the component’s value changes How to handle disabled state 📦 Common Built-in Examples: <input> and <select> already implement ControlValueAccessor You implement it when creating custom form controls 🔧 Key Methods in the Interface Method Purpose writeValue(obj: any) Called by Angular to set the value in the component registerOnChange(fn: any) Passes a function to call when the component value ch...

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