Initial commit

Author: alexlanz

.gitignore

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+# Basic
+.DS_Store
+
+# IDE
+/.idea
+/.vscode

__test__/pagination.test.ts

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+import { calculatePagination } from '../index'
+
+it('should return no pagination if not enough items are given', () => {
+  const page = 1
+  const size = 5
+  const total = 2
+  const pagination = calculatePagination(page, size, total)
+
+  expect(pagination).toBeNull()
+})
+it('should return only a few pages', () => {
+  const page = 2
+  const size = 5
+  const total = 15
+  const pagination = calculatePagination(page, size, total)
+
+  expect(pagination?.pages).toHaveLength(3)
+
+  expect(pagination.pages[0].number).toBe(1)
+  expect(pagination.pages[0].isCurrentPage).toBeFalsy()
+  expect(pagination.pages[1].number).toBe(2)
+  expect(pagination.pages[1].isCurrentPage).toBeTruthy()
+  expect(pagination.pages[2].number).toBe(3)
+  expect(pagination.pages[2].isCurrentPage).toBeFalsy()
+})
+it('should return the maximum number of pages', () => {
+  const page = 5
+  const size = 5
+  const total = 50
+  const maxPages = 5
+  const pagination = calculatePagination(page, size, total, maxPages)
+
+  expect(pagination?.pages).toHaveLength(5)
+
+  expect(pagination.pages[0].number).toBe(3)
+  expect(pagination.pages[0].isCurrentPage).toBeFalsy()
+  expect(pagination.pages[1].number).toBe(4)
+  expect(pagination.pages[1].isCurrentPage).toBeFalsy()
+  expect(pagination.pages[2].number).toBe(5)
+  expect(pagination.pages[2].isCurrentPage).toBeTruthy()
+  expect(pagination.pages[3].number).toBe(6)
+  expect(pagination.pages[3].isCurrentPage).toBeFalsy()
+  expect(pagination.pages[4].number).toBe(7)
+  expect(pagination.pages[4].isCurrentPage).toBeFalsy()
+})
+it('should disable the previous link', () => {
+  const page = 1
+  const size = 5
+  const total = 10
+  const pagination = calculatePagination(page, size, total)
+
+  expect(pagination.previous.number).toBe(1)
+  expect(pagination.previous.isDisabled).toBeTruthy()
+
+  expect(pagination.next.number).toBe(2)
+  expect(pagination.next.isDisabled).toBeFalsy()
+
+  expect(pagination?.pages[0].isCurrentPage).toBeTruthy()
+  expect(pagination?.pages[1].isCurrentPage).toBeFalsy()
+})
+it('should disable the next link', () => {
+  const page = 2
+  const size = 5
+  const total = 10
+  const pagination = calculatePagination(page, size, total)
+
+  expect(pagination.previous.number).toBe(1)
+  expect(pagination.previous.isDisabled).toBeFalsy()
+
+  expect(pagination.next.number).toBe(2)
+  expect(pagination.next.isDisabled).toBeTruthy()
+
+  expect(pagination?.pages[0].isCurrentPage).toBeFalsy()
+  expect(pagination?.pages[1].isCurrentPage).toBeTruthy()
+})

index.ts

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+const calculateVisiblePages = (
+  page: number,
+  total: number,
+  maxPages: number
+): number[] => {
+  const range = Math.floor(maxPages / 2)
+  let lowerBound = 1
+  let lowerBoundRest = 0
+  let upperBound = total
+  let upperBoundRest = 0
+
+  if (page - range >= 1) {
+    lowerBound = page - range
+  } else {
+    lowerBoundRest = (page - range - 1) * -1
+  }
+
+  if (page + range <= total) {
+    upperBound = page + range
+  } else {
+    upperBoundRest = (total - range - page) * -1
+  }
+
+  if (upperBoundRest > 0) {
+    lowerBound =
+      lowerBound - upperBoundRest > 0 ? lowerBound - upperBoundRest : 1
+  }
+
+  if (lowerBoundRest > 0) {
+    upperBound =
+      upperBound + lowerBoundRest < total ? upperBound + lowerBoundRest : total
+  }
+
+  const pages = []
+
+  for (let i = lowerBound; i <= upperBound; i++) {
+    pages.push(i)
+  }
+
+  return pages
+}
+
+const calculatePagination = (
+  page: number,
+  size: number,
+  total: number,
+  maxPages: number = 5
+): {
+  previous: {
+    number: number
+    isDisabled: boolean
+  }
+  next: {
+    number: number
+    isDisabled: boolean
+  }
+  pages: {
+    number: number
+    isCurrentPage: boolean
+  }[]
+} | null => {
+  if (total <= size) {
+    return null
+  }
+
+  const lastPage = Math.ceil(total / size)
+  const isCurrentTheFirstPage = page === 1
+  const isCurrentTheLastPage = page === lastPage
+
+  return {
+    previous: {
+      number: isCurrentTheFirstPage ? 1 : page - 1,
+      isDisabled: isCurrentTheFirstPage,
+    },
+    next: {
+      number: isCurrentTheLastPage ? lastPage : page + 1,
+      isDisabled: isCurrentTheLastPage,
+    },
+    pages: calculateVisiblePages(page, lastPage, maxPages).map(
+      (visiblePage) => {
+        return {
+          number: visiblePage,
+          isCurrentPage: visiblePage === page,
+        }
+      }
+    ),
+  }
+}
+
+export { calculatePagination }

readme.md

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+Pagination
+==========
+