Node.js：尝试侦听设置为动态函数的变量时出错

First off, apologies for my lack of knowledge with node, I'm probably making some big noob mistakes. In the following example I'm trying to set a variable to a function that has a continuously changing output, listen for a change in that variable, and output the new results whenever the value of the variable changes. This is the following error that I'm receiving and I don't have a clue what to do about it.First off, apologies for my lack of knowledge w