npm install

First command line argument is where to begin, the second is where to stop.

node index.js 1 25000

It is possible that Fangraphs ReCaptcha's the script if you give it a large input size.

You will see something along the lines of:

RECAPTCHA detected at id: 1
Have you solved it? (Y/n):

Navigate to your browser and go to Fangraphs.com and go to a player page, manually click the captcha, come back to the program and type Y to continue. Depending on how much it cares, you might need to wait a while before continuing. You can restart the program with new paramaters picking up where you left off.