Growing Line Animation

How Do I do a growing line animation Like the growing dotted line in this video. The line can be solid.

Draw an advanced outline. Toggle width handles. Hide all the other handles to make selection easier. Right click the second width vertex of the outline (light purple dot) and choose cusp after:flat from the menu. Now you can move the second width vertex along the outline to make the outline appear and you can link a circle or any other object to the outline that follows along with the second width vertex.