Adjustable starting pages

readme.md

@@ -24,7 +24,9 @@ Second, you can call the calculate function by passing the following information
 - `page`: The current page
 - `size`: The amount of items shown per page
 - `total`: The amount of total items in the list/collection
-- `maxPages`: The maximum amount of pages that should be shown (default: 5)
+- `config`: A configuration object containing the following possible configuration values:
+  - `firstPage`: The first page of the pagination (default: 1)
+  - `maxPages`: The maximum amount of pages that should be shown (default: 5)
 
 In return, you receive an object with all relevant information:
 

src/__test__/pagination-with-first-page-0.test.ts

@@ -0,0 +1,84 @@
+import { calculatePagination } from '../index'
+
+it('should return no pagination if not enough items are given', () => {
+  const page = 0
+  const size = 5
+  const total = 2
+  const pagination = calculatePagination(page, size, total, { firstPage: 0 })
+
+  expect(pagination).toBeNull()
+})
+it('should return only a few pages', () => {
+  const page = 1
+  const size = 5
+  const total = 15
+  const pagination = calculatePagination(page, size, total, { firstPage: 0 })
+
+  expect(pagination).not.toBeNull()
+  expect(pagination?.pages).toHaveLength(3)
+
+  expect(pagination?.pages[0].number).toBe(0)
+  expect(pagination?.pages[0].isCurrent).toBeFalsy()
+  expect(pagination?.pages[1].number).toBe(1)
+  expect(pagination?.pages[1].isCurrent).toBeTruthy()
+  expect(pagination?.pages[2].number).toBe(2)
+  expect(pagination?.pages[2].isCurrent).toBeFalsy()
+})
+it('should return the maximum number of pages', () => {
+  const page = 4
+  const size = 5
+  const total = 50
+  const maxPages = 5
+  const pagination = calculatePagination(page, size, total, {
+    firstPage: 0,
+    maxPages: maxPages,
+  })
+
+  expect(pagination).not.toBeNull()
+  expect(pagination?.pages).toHaveLength(5)
+
+  expect(pagination?.pages[0].number).toBe(2)
+  expect(pagination?.pages[0].isCurrent).toBeFalsy()
+  expect(pagination?.pages[1].number).toBe(3)
+  expect(pagination?.pages[1].isCurrent).toBeFalsy()
+  expect(pagination?.pages[2].number).toBe(4)
+  expect(pagination?.pages[2].isCurrent).toBeTruthy()
+  expect(pagination?.pages[3].number).toBe(5)
+  expect(pagination?.pages[3].isCurrent).toBeFalsy()
+  expect(pagination?.pages[4].number).toBe(6)
+  expect(pagination?.pages[4].isCurrent).toBeFalsy()
+})
+it('should disable the previous link', () => {
+  const page = 0
+  const size = 5
+  const total = 10
+  const pagination = calculatePagination(page, size, total, { firstPage: 0 })
+
+  expect(pagination).not.toBeNull()
+
+  expect(pagination?.previous.number).toBe(0)
+  expect(pagination?.previous.isDisabled).toBeTruthy()
+
+  expect(pagination?.next.number).toBe(1)
+  expect(pagination?.next.isDisabled).toBeFalsy()
+
+  expect(pagination?.pages[0].isCurrent).toBeTruthy()
+  expect(pagination?.pages[1].isCurrent).toBeFalsy()
+})
+it('should disable the next link', () => {
+  const page = 1
+  const size = 5
+  const total = 10
+  const pagination = calculatePagination(page, size, total, { firstPage: 0 })
+
+  expect(pagination).not.toBeNull()
+
+  expect(pagination?.previous.number).toBe(0)
+  expect(pagination?.previous.isDisabled).toBeFalsy()
+
+  expect(pagination?.next.number).toBe(1)
+  expect(pagination?.next.isDisabled).toBeTruthy()
+
+  expect(pagination?.pages[0].isCurrent).toBeFalsy()
+  expect(pagination?.pages[1].isCurrent).toBeTruthy()
+})

src/__test__/pagination.test.ts → src/__test__/pagination-with-first-page-1.test.ts

@@ -29,7 +29,9 @@ it('should return the maximum number of pages', () => {
   const size = 5
   const total = 50
   const maxPages = 5
-  const pagination = calculatePagination(page, size, total, maxPages)
+  const pagination = calculatePagination(page, size, total, {
+    maxPages: maxPages,
+  })
 
   expect(pagination).not.toBeNull()
   expect(pagination?.pages).toHaveLength(5)

src/index.ts

@@ -1,12 +1,13 @@
 const calculateVisiblePages = (
   page: number,
-  total: number,
+  firstPage: number,
+  lastPage: number,
   maxPages: number
 ): number[] => {
   const range = Math.floor(maxPages / 2)
-  let lowerBound = 1
+  let lowerBound = firstPage
   let lowerBoundRest = 0
-  let upperBound = total
+  let upperBound = lastPage
   let upperBoundRest = 0
 
   if (page - range >= 1) {
@@ -15,20 +16,22 @@ const calculateVisiblePages = (
     lowerBoundRest = (page - range - 1) * -1
   }
 
-  if (page + range <= total) {
+  if (page + range <= lastPage) {
     upperBound = page + range
   } else {
-    upperBoundRest = (total - range - page) * -1
+    upperBoundRest = (lastPage - range - page) * -1
   }
 
   if (upperBoundRest > 0) {
     lowerBound =
-      lowerBound - upperBoundRest > 0 ? lowerBound - upperBoundRest : 1
+      lowerBound - upperBoundRest > 0 ? lowerBound - upperBoundRest : firstPage
   }
 
   if (lowerBoundRest > 0) {
     upperBound =
-      upperBound + lowerBoundRest < total ? upperBound + lowerBoundRest : total
+      upperBound + lowerBoundRest < lastPage
+        ? upperBound + lowerBoundRest
+        : lastPage
   }
 
   const pages = []
@@ -44,7 +47,10 @@ const calculatePagination = (
   page: number,
   size: number,
   total: number,
-  maxPages = 5
+  config?: {
+    firstPage?: number
+    maxPages?: number
+  }
 ): {
   previous: {
     number: number
@@ -63,20 +69,23 @@ const calculatePagination = (
     return null
   }
 
-  const lastPage = Math.ceil(total / size)
-  const isCurrentTheFirstPage = page === 1
+  const firstPage = config?.firstPage ?? 1
+  const maxPages = config?.maxPages ?? 5
+
+  const lastPage = Math.ceil(total / size) + (firstPage - 1)
+  const isCurrentTheFirstPage = page === firstPage
   const isCurrentTheLastPage = page === lastPage
 
   return {
     previous: {
-      number: isCurrentTheFirstPage ? 1 : page - 1,
+      number: isCurrentTheFirstPage ? firstPage : page - 1,
       isDisabled: isCurrentTheFirstPage,
     },
     next: {
       number: isCurrentTheLastPage ? lastPage : page + 1,
       isDisabled: isCurrentTheLastPage,
     },
-    pages: calculateVisiblePages(page, lastPage, maxPages).map(
+    pages: calculateVisiblePages(page, firstPage, lastPage, maxPages).map(
       (visiblePage) => {
         return {
           number: visiblePage,