Pagination Class for javascript

Pagination.js

var Pagination = function(list, itemsPerPage) {
  this.list = list;
  this.itemsPerPage = itemsPerPage;
  this.currentPageNumber = null;
  this.currentPageIndex = null;
  this.currentPageItems = [];
  this.totalItems = this.list.length;
  this.totalPages = Math.ceil(this.totalItems / this.itemsPerPage );

  this.toFirstPage();
  
  if(this.itemsPerpage > this.totalItems) {
    throw Error("itemsPerPage should be less than the length of the list");  
  }

}

Pagination.prototype.toLastPage = function() {
    this.currentPageNumber = this.totalPages;
    this.currentPageIndex = this.totalPages - 1;
    this.currentPageItems = this.getCurrentPageItems();
}

Pagination.prototype.toFirstPage = function() {
    this.currentPageNumber = 1;
    this.currentPageIndex = 0;
    this.currentPageItems = this.getCurrentPageItems();
}

Pagination.prototype.hasNext = function() {
   return (this.currentPageNumber < this.totalPages && this.currentPageNumber >= 0);
}

Pagination.prototype.hasPrevious = function() {
   return (this.currentPageNumber <= 1) ? false : true;
}

Pagination.prototype.toPageNumber = function(pageNumber) {
  if(pageNumber <= 0)
  {
    throw Error("pageNumber should be greater than 0");
  }
  else if(pageNumber > this.totalPages)
  {
    throw Error("pageNumber can't be greater than totalPages");
  }
  
  this.currentPageNumber = pageNumber;
  this.currentPageIndex = pageNumber - 1;
  this.currentPageItems = this.getCurrentPageItems();
}

Pagination.prototype.toNextPage = function() {
  this.currentPageNumber += 1;
  this.currentPageIndex = this.currentPageNumber - 1;
  this.currentPageItems = this.getCurrentPageItems();
  if(!this.hasNext())
  {
    throw Error("You can't go further in the next stepping");
  }
}

Pagination.prototype.toPreviousPage = function() {
  this.currentPageNumber -= 1;
  this.currentPageIndex = this.currentPageNumber - 1;
  this.currentPageItems = this.getCurrentPageItems();
  if(!this.hasPrevious())
  {
    throw Error("You can't go further in the previous stepping");
  }
}


Pagination.prototype.getCurrentPageItems = function() {
  return this.list.slice(this.currentPageIndex * this.itemsPerPage , this.itemsPerPage + this.currentPageIndex *  this.itemsPerPage);
}

pagination.spec.js

describe('Pagination Class',function(){
  var list, pagination;
  beforeEach(function(){
      list = [1,2,3,4,5,6,7,8,9,10];
      pagination = new Pagination(list, 3);
  });
 
  it('should Pagination Class with the correct properties values',function(){
    expect(pagination.totalItems).toEqual(10);
    expect(pagination.totalPages).toEqual(4);
    expect(pagination.currentPageNumber).toEqual(1);
    expect(pagination.currentPageIndex).toEqual(0);
  });
  
  it('should slice the items correctly when toFirstPage',function(){
      expect(pagination.currentPageItems).toEqual([1,2,3]);
  });
  
  it('should slice the items correctly when toLastPage',function(){
      pagination.toLastPage();
      expect(pagination.currentPageItems).toEqual([10]);
  });
  
    it('should slice the items correctly when pageNumber n',function(){
      pagination.toPageNumber(1);
      expect(pagination.currentPageItems).toEqual([1,2,3]);
      
      pagination.toPageNumber(2);
      expect(pagination.currentPageItems).toEqual([4,5,6]);
      
      pagination.toPageNumber(3);
      expect(pagination.currentPageItems).toEqual([7,8,9]);
      
      pagination.toPageNumber(4);
      expect(pagination.currentPageItems).toEqual([10]);
  });
  
    it('should slice the items correctly when nextPage n',function(){
      pagination.toFirstPage();
      pagination.toNextPage();
      expect(pagination.currentPageNumber).toEqual(2);
      expect(pagination.currentPageItems).toEqual([4,5,6]);
  });
  
  it('should check hasNext  and hasPrevious correctly',function(){
      pagination.toFirstPage();
      expect(pagination.hasNext()).toBe(true);
      expect(pagination.hasPrevious()).toBe(false);
      
      pagination.toLastPage();
      expect(pagination.hasNext()).toBe(false);
      expect(pagination.hasPrevious()).toBe(true);
      
      pagination.toPageNumber(2);
      expect(pagination.hasNext()).toBe(true);
      expect(pagination.hasPrevious()).toBe(true);
      
      pagination.toPageNumber(3);
      expect(pagination.hasNext()).toBe(true);
      expect(pagination.hasPrevious()).toBe(true);
      
      pagination.toPageNumber(4);
      expect(pagination.hasNext()).toBe(false);
      expect(pagination.hasPrevious()).toBe(true);
  });
  
   it('pagination should have no loop in interations',function(){
      pagination.toFirstPage();
      expect(function() {
        pagination.toPreviousPage();
      }).toThrow();
      
      pagination.toLastPage();
      expect(function() {
        pagination.toNextPage();
      }).toThrow();
      
   });
});