For Angularjs or Angular 1.x posts, it will be stated 1.x explicitly, else it’s always the latest version of Angular. Use Case Let’ say you have a that will display blogger details and her posts. Blogger component will gets the list of posts from API. blogger component Instead of writing the logic of displaying the posts in the blogger component, you want to reuse the that is created by your teammate, what you need to do is pass it the posts . posts component data The posts component will then by category and display accordingly, like this: group the posts blogger component Isn’t That Easy? It might look easy at the first glance. Most of the time we will initiate all the process during our component initialization time — during life cycle hook (refer for more details on component life cycle hook). ngOnInit here In our case, you might think that we should run the post grouping logic during of the posts component. ngOnInit However, because the data is coming from server, when the blogger component passes the data to posts component, the posts component before the data get updated. Your post grouping logic will not be fired. posts posts ngOnInit is already fired How can we solve this? Please read further in my Scotch post. _Let's start with a common use case. You have some data you get from external source (e.g. by calling API). You want to…_scotch.io 3 Ways to Pass Async Data to Angular 2+ Child Components