What is Two-Way Data Binding in Angular?
💡 Concept Name
Two-Way Data Binding – A mechanism in Angular that allows automatic synchronization between the component class and the template.
📘 Quick Intro
Two-way data binding in Angular enables your view (template) and your component (class) to stay in sync automatically. It combines property binding and event binding using the special syntax [(ngModel)].
🧠 Analogy / Short Story
Imagine a thermostat—you set the temperature, and the room adjusts. If the room changes temperature, the thermostat reflects it. That's two-way binding—changes in one place reflect in the other.
🔧 Technical Explanation
- 🔁 Combines property binding and event binding in one directive.
- 🔧 Requires importing the
FormsModulein your Angular module. - 📌 Uses the syntax
[(ngModel)]to bind data both ways. - 👁️🗨️ Automatically reflects updates from component to view and vice versa.
- 📍 Commonly used in forms and inputs where user data must sync with the model.
🎯 Purpose & Use Case
- ✅ Building dynamic forms
- ✅ Instant updates between UI and component
- ✅ Editable user profile components
- ✅ Interactive controls (e.g., sliders, toggles)
💻 Real Code Example
// app.component.ts
export class AppComponent {
username: string = "";
}<!-- app.component.html -->
<input [(ngModel)]="username" placeholder="Enter name" />
<p>Hello, {{ username }}</p>
❓ Interview Q&A
Q1: What is two-way data binding in Angular?
A: It synchronizes data between the view and the component.
Q2: What syntax is used for two-way binding?
A: [(ngModel)]
Q3: What modules are needed for two-way binding?
A: FormsModule must be imported in your Angular module.
Q4: Can two-way binding be used on custom components?
A: Yes, with input/output decorators and control value accessors.
Q5: Why is two-way binding useful?
A: It reduces boilerplate and keeps UI and data in sync.
📝 MCQs
Q1. Which directive is used for two-way binding?
- ngIf
- ngModel
- ngBind
- ngFor
Q2. What syntax is used for two-way data binding?
- {{ngModel}}
- (ngModel)
- [ngModel]
- [(ngModel)]
Q3. What must be imported to use ngModel?
- ReactiveFormsModule
- HttpClientModule
- FormsModule
- CommonModule
Q4. Two-way binding is a combination of which two bindings?
- Interpolation & Directive
- Property & Event
- Model & View
- Component & Template
Q5. Where is two-way binding mostly used?
- Routing
- Animations
- Forms
- Services
💡 Bonus Insight
Two-way binding is powerful but should be used judiciously. For large forms, consider ReactiveFormsModule for better scalability and control.
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