d3检索csv文件在javascript控制台中返回Nan

I'm just learning how to use d3. I'm having an issue when trying to retrieve a .cvs/excel file. At line 13 I get a console reading of "4 Nan", or "4 undefined, undefined". I might have the location of books.csv in the wrong location. It is located "xampp\htdocs\books.csv" along with my html file and d3.js.. The row and columns are 5 * 2. Any questions or help is much appreciated!I'm just learning how to use d3. I'm having an