Explain the difference between “Constructor” and “ngOnInit”

• The Constructor is a default method of the class that is executed when the class is instantiated and ensures proper initialization of fields in the class and its subclasses.
• ngOnInit is a life cycle hook called by Angular to indicate that Angular is done creating the component. We have to import OnInit in order to use like this (actually implementing OnInit is not mandatory but considered good practice).

Mostly we use ngOnInit for all the initialization/declaration and avoid stuff to work in the constructor. The constructor should only be used to initialize class members but shouldn’t do actual “work”.