How does the Back button in a web browser work?

Question

I searched the Web about this question but I found nothing:

What is the logic of the back button? What is happening when we hit the back button on a Web browser?

Answer 1

I think the easiest way to explain this is in pseudocode:

class Page:
    String url, ...
    Page previous, next # implements a doubly-linked list

class History:
    Page current # current page

    void back():
        if current.previous == null:
            return
        current = current.previous
        refresh()

    void forward():
        if current.next == null:
            return
        current = current.next
        refresh()

    void loadPage(Page newPage):
        newPage.previous = current
        current.next = newPage # remove all the future pages
        current = current.next
        display(current)