Explain the difference between constructor and ngOnInit in Angular.

• What is purpose of asking this question :
  • Interviewers often ask this question to gauge the candidate’s understanding of Angular lifecycle hooks and their ability to properly structure and initialize components in an Angular application.
  • Understanding the difference between constructor and ngOnInit is important for creating efficient and maintainable code in Angular, as it helps ensure that components are properly initialized and set up for use.
• Your answer should be:
  • A constructor is a special method in a class that is automatically called when an instance of the class is created. It is mainly used for initializing variables and dependencies.
  • On the other hand, ngOnInit is a lifecycle hook in Angular that is called after the constructor when the component is initialized.
  • It is typically used for initializing component properties and making API calls. In summary, the constructor is used for setting up the class instance, while ngOnInit is used for setting up the component.
• Explore various use cases for ngOnInit in Angular components, such as handling asynchronous tasks or interacting with external services.
  • For example, a constructor in an Angular component could be used to directly make API calls to fetch data, bypassing the recommended use of services for data retrieval. This could result in tightly coupling the component to external dependencies and making it harder to test and maintain. On the other hand, utilizing ngOnInit for such tasks allows for better separation of concerns and easier unit testing of the component’s functionality.