Assuming the wiki is still functional, under the Entry object in the Memento JavaScript Library page in the Scripting section, there is no mention of a linksFrom() method of that object.
That said, the Releases page indicates that such a method was added, so I guess it probably exists, but its arguments, return values, and so on are just not documented in the main place one would look for it in the wiki.
This makes me very sad.
Don't forget the parentheses when referring to it, because if they weren't there, people will think you're referring to one of the object's properties rather than a method. It's linksFrom(). Make sure the object your trying to call it from is an Entry object, assuming the method exists, as suggested by Mmm and the Releases page.