call initialize method in ngOnInit or constructor

Question

Im very new to Angular 4,

Can you tell me what is the different between call a method like initializeMyObj() in constructor than ngOnInit in ts file?

Thank you

Answer 1

The major difference is that constructor is typescript construct whereas ngOnInit is life cycle hook of component and directive.

Constructor is used to initialize the component. At this time, @Input bound properties are not initialized.

On the other hand ngOnInit is called once after constructor and ngOnChange. At this time, the component is initialized and properties are bound.

@Component({
...
})
export class MyComp{
    @Input() someprop;
    constructor(){
        console.log(someprop); //undefined
    }
    ngOnInit(){
        console.log(someprop); 
    }
}