| Constructor | ngOnInit |
|---|---|
| Typescript feature nothing to do with Angular | One of the Angular life cycle hook method |
| constructor is transformed to function with the same name as class created | ngOnInit being added to prototype of the class created |
| Called by Javascript Engine | Called by Angular |
| Constructor is automaticlly called at the time of creating object of the class | Invoked by Angular when everything in the component is ready |
| Used for Injecting dependencies | Actual business logic performed here |
| Not everything in component is initialized at the time of invocation | Everything is ready at the time of invocation |
Thanks to, Angular js Wiki