title: What is the best way to call a service in Angular 2
body: <p>I am using angular 2 for fetching data from an API with an <strong>Injectable</strong> service written for it.Should I call my service in the <strong>constructor</strong> or <strong>ngoninit</strong> in the component  where i am going to utilize  my data.
  Can someone explain the best way to use constructor and ngoninit hook in angular 2 like constructor is used for instantiating services.</p>