Using Angular markup like {{hash}} in an href attribute will make the link go to the wrong URL if the user clicks it before Angular has a chance to replace the {{hash}} markup with its value. Until Angular replaces the markup the link will be broken and will most likely return a 404 error. The ngHref directive solves this problem.

The wrong way to write it:

<a href="http://www.gravatar.com/avatar/{{hash}}">link1</a>

The correct way to write it:

<a ng-href="http://www.gravatar.com/avatar/{{hash}}">link1</a>