How can i disable backspace navigation with javascript

I have written an app in javascript with 2 divs, on load the 1st is visible and the 2nd is hidden. When a user completes the 1st div they then procced to the 2nd div, for usability if a user wants to go back i would like them to be able to use the backspace.

i have the code to catch the keypress of the backspace on the 2nd div and use it to go back to the 1st div.

However when i press backspace, the browser navigates to my previous page rather than to my 1st div.

thanks chris1990