Javascript issue: can t get strings to work as method

I'm struggeling with this little piece of code

 //originalNode.GetFloat(Transform.Position X);

I`m trying to create a script where I type in the arguments of a node I want to copy to a different node. But I got stuck with this part.

argument is an array in wich I stored the 2 values, it does not contain the "." as seen in the reference

The commented code is how it should look, I got it from the reference API