class EBook $\{$

$//$ Constructor takes two arguments:

$//*$ First arg is a string with the whole text of the book

$//*$ Second arg is the number of characters contained in a single page of the book

$//$ Instances have a $`$next$`$ method:

$//*$ It takes no args and returns the next page of the book

$//*$ If the next page is empty because we have reached the end, return null instead

$//$ Example of usage:

$//$ const ebook $=$ new EBook$(\text{'}$abcdefg$\text{'},3)$

$//$ ebook.next$()//$ returns "abc"

$//$ ebook.next$()//$ returns "def"

$//$ ebook.next$()//$ returns $"$g$"$

$//$ ebook.next$()//$ returns null

$//$ HINT: remember about the $`$slice$`$ method which strings and arrays have

$//$ Feel free to implement $`$back$`,$ although this is not required nor graded

$\}$