angular - Why use "?" operator in template binding?

Question

When I use ?, the binding works well. If I remove it, it doesn't show anything in the view.

<span class="subhead">{{project?.category}}</span>

Can you please tell me the difference? Is it a good practice to use it this way?

Answer 1

When Angular renders the view before project got a value assigned, it causes an exception. ?. stops evaluating when project is null or undefined, which usually happens when data is fetched async, for example from the server which can take quite some time.

The next time change detection recognizes a change, the bindings will be re-evaluated. When project then has a value it will bind project.category.