Scraping Data using JavaScript

I am working on a project where I want to scrape out data from a website whenever the value of the range slider is changed by the user and compare it with the actual data.

The tasks are:

1. Scrape the actual data(initial value) 2.Scrape out the base data(the value changed by the user)
2. I am supposed to extract the base data for each change in value done by the user and compare it with the actual data and store it in local directory (CONDITION: Must be done only using JavaScript)

The slider is present within an iframe.

Can someone please suggest any approach/packages for doing this?