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Question 1: Can you explain how two-way data binding works in Angular and give an example of how you have used it in a project?

A great answer would be that two-way data binding, in Angular, is a pre-built feature that synchronizes data between the view and the model. When the model changes, the view updates automatically, and when the view changes, the model updates automatically.

For example, consider a form that displays and updates data from a backend. Two-way data binding can bind form fields to a model, automatically updating the model when users change the fields. When the backend sends new data, the form fields update accordingly. Additionally, validation can be easily incorporated to display or hide error messages based on the form's state.

An okay answer would show basic knowledge without detail. The developer might understand that changes in the view update the model and vice versa but may require guidance on best practices and effective use in projects.

Question 2: Can you explain the difference between a component and a directive in Angular?

A great answer would state that a component in Angular is a class controlling a portion of the DOM through a template. It has a defined lifecycle and can accept inputs and emit events.

A directive, however, directly manipulates the DOM by adding behavior to existing elements without having its own template or lifecycle. A component example might be a form with fields and a submit button, whereas a directive example could be one that highlights an element upon hover.

A good answer would note a component as a class controlling a view (portion of the screen) with an associated HTML template defining its layout and content. A directive would be described as adding additional behavior or functionality to existing components or elements. Such a developer might need additional support to fully grasp implementation details.

Question 3: Can you show an example of how to create a custom directive in Angular?

In this example, we're importing Directive, ElementRef, and HostListener decorators from the @angular/core module, creating a directive called MakeUppercaseDirective. This directive listens for input events and automatically transforms input text to uppercase.

To use the directive, you add its selector (appMakeUppercase) to an input element within the template.

A good answer might explain the concept without showing actual code. Such a developer might benefit from support in understanding the creation and use of custom directives and decorators (Directive, ElementRef, HostListener).

View code snippet example here

Question 4: Can you show an example of how to create a form in Angular with two-way data binding and validation?

In this example, the form is defined using the formGroup directive, binding to a formData object in the component class. Fields use formControlName to connect to formData properties. Two-way data binding is achieved using [(ngModel)], binding field values to component class properties (like the user object).

Validation employs the required attribute, and error messages appear via *ngIf directives checking the invalid and touched states of each control. The submit button disables automatically if the form becomes invalid.

To use this snippet, import ReactiveFormsModule and create the necessary formGroup in your component class.

View Angular Form Code snippet here
View formGroup creation snippet here

An OK Angular developer might write basic code but struggle to explain [(ngModel)] usage and validation handling clearly.

Question 5: Can you explain how dependency injection works in Angular?

Dependency injection in Angular provides components with dependencies at runtime, enabling loosely coupled components and easy substitution of implementations.

Angular’s hierarchical injector system lets components request dependencies from parent injectors or the root injector. Dependencies, defined using providers, can be registered at various levels (component, module, root). For example, injecting Angular's HttpClient service allows components to perform HTTP requests effectively.