Pagination like github

pagination.js

function getDisplayedPages(currentPage, pagesArr) {
  /*
  Will return 5 total pages, with current page in the middle.
  */
  var lastPage = pagesArr.length;
  var first = (Math.sign(currentPage - 3) === -1) ? 0 : currentPage - 3;
  var last = currentPage + 2;
  
  if (currentPage > lastPage) return;
  
  if (last <= 5) {
    last = 5;
  }
  
  if (last >= lastPage) {
    first = first - (last - lastPage);
    last = lastPage;
  }
  
  console.log('currentPage', currentPage);
  console.log('first', first);
  console.log('last', last);
  
  return pagesArr.slice(first, last);
}

var currentPage = 7;
var pagesArr = [1,2,3,4,5,6,7,8,9,10];

var displayedPages = getDisplayedPages(currentPage, pagesArr);

console.log(displayedPages);