javascript 71 lines · 9 steps

A closure-based pagination helper in JS

A factory function keeps the current page private and exposes a small read/navigate API that the DOM renders against.

Explained by highlit
Intermediate closures encapsulation factory-function getters dom-rendering
1function usePagination(items, pageSize = 10) {
2 let currentPage = 1;
3 const totalPages = Math.max(1, Math.ceil(items.length / pageSize));
4 
5 function clamp(page) {
6 return Math.min(Math.max(page, 1), totalPages);
7 }
8 
9 function slice() {
10 const start = (currentPage - 1) * pageSize;
11 return items.slice(start, start + pageSize);
12 }
13 
14 return {
15 get page() {
16 return currentPage;
17 },
18 get totalPages() {
19 return totalPages;
20 },
21 get hasPrevious() {
22 return currentPage > 1;
23 },
24 get hasNext() {
25 return currentPage < totalPages;
26 },
27 get items() {
28 return slice();
29 },
30 goTo(page) {
31 currentPage = clamp(page);
32 return slice();
33 },
34 next() {
35 return this.goTo(currentPage + 1);
36 },
37 previous() {
38 return this.goTo(currentPage - 1);
39 },
40 };
41}
42 
43function renderControls(pager, container) {
44 container.innerHTML = `
45 <button data-action="prev" ${pager.hasPrevious ? "" : "disabled"}>Previous</button>
46 <span>Page ${pager.page} of ${pager.totalPages}</span>
47 <button data-action="next" ${pager.hasNext ? "" : "disabled"}>Next</button>
48 `;
49 
50 container.querySelector('[data-action="prev"]').onclick = () => {
51 pager.previous();
52 renderList(pager);
53 renderControls(pager, container);
54 };
55 container.querySelector('[data-action="next"]').onclick = () => {
56 pager.next();
57 renderList(pager);
58 renderControls(pager, container);
59 };
60}
61 
62function renderList(pager) {
63 const list = document.getElementById("list");
64 list.replaceChildren(
65 ...pager.items.map((item) => {
66 const li = document.createElement("li");
67 li.textContent = item.title;
68 return li;
69 })
70 );
71}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1A factory function plus closure hides mutable state behind a controlled, read-only surface.
  2. 2Getters let callers observe derived state like hasNext without exposing the underlying variable.
  3. 3Keeping navigation and rendering separate means the UI just reacts to whatever the pager reports.

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