Method and code for obtaining external function names in js class

For example, if we want to set a method in a class, we can save it in a class variable according to the call-in method. When needed, we can obtain it by accessing the class variable.
Usually if we generate an instance
For example: var temp=new TopnetTree();
If we pass in a method by setting properties, we will find that what is passed in is the content of a function, not the function name.
For example =fnTest; //fnTest is a function

So I wrote a method to implement this function.
Use arguments to judge the content passed:
Implement the following functions:
The content passed is empty and no content is executed
Passing a parameter means it is a function without parameters
Passing multiple parameters means the first parameter bit function name, followed by each parameter.