Extracting keyframe length from Library MC

Is there an easy way to extract the lenght of keyframes from a Library object? At this moment I simply create a new instance of it and read it out, for example

anidurin = new obj1_elite_alien().totalFrames;

But that also literally makes them ‘play’ and perform the actions within their timeline, and I can’t have that.

So, any other better way to do this or any way to immediately remove the invisible new object after I extracted the frame lenght ‘anidurin’?

tnx for suggestions
P.