Deprecation Guide for Using this.get('template')

Prior to 1.13, developers had to check for the existance of the internal template property to determine the existance of a yielded block. This is being deprecated in favor of using the new hasBlock property within your templates.

Determining if a block has been provided from JavaScript

Currently the hasBlock property is not made available from the JavaScript component object, so there is no clean alternative for checking whether a block has been passed. See the JavaScript hasBlock RFC for discussion on making this information available in the future, as well as possible workarounds.