javascript 63 lines · 8 steps

Building a compound Accordion in React

Two React contexts let an Accordion share open state and per-item IDs across loosely coupled subcomponents.

Explained by highlit
React Intermediate context compound-components state-management accessibility component-composition
1import { createContext, useContext, useState, useId } from "react";
2 
3const AccordionContext = createContext(null);
4const ItemContext = createContext(null);
5 
6export function Accordion({ children, allowMultiple = false }) {
7 const [openIds, setOpenIds] = useState(() => new Set());
8 
9 const toggle = (id) => {
10 setOpenIds((prev) => {
11 const next = new Set(allowMultiple ? prev : []);
12 if (prev.has(id)) next.delete(id);
13 else next.add(id);
14 return next;
15 });
16 };
17 
18 return (
19 <AccordionContext.Provider value={{ openIds, toggle }}>
20 <div className="accordion">{children}</div>
21 </AccordionContext.Provider>
22 );
23}
24 
25Accordion.Item = function AccordionItem({ children }) {
26 const id = useId();
27 return (
28 <ItemContext.Provider value={id}>
29 <div className="accordion-item">{children}</div>
30 </ItemContext.Provider>
31 );
32};
33 
34Accordion.Header = function AccordionHeader({ children }) {
35 const id = useContext(ItemContext);
36 const { openIds, toggle } = useContext(AccordionContext);
37 const isOpen = openIds.has(id);
38 
39 return (
40 <button
41 type="button"
42 className="accordion-header"
43 aria-expanded={isOpen}
44 aria-controls={`panel-${id}`}
45 onClick={() => toggle(id)}
46 >
47 {children}
48 <span aria-hidden>{isOpen ? "\u2212" : "+"}</span>
49 </button>
50 );
51};
52 
53Accordion.Panel = function AccordionPanel({ children }) {
54 const id = useContext(ItemContext);
55 const { openIds } = useContext(AccordionContext);
56 if (!openIds.has(id)) return null;
57 
58 return (
59 <div id={`panel-${id}`} role="region" className="accordion-panel">
60 {children}
61 </div>
62 );
63};
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Compound components share state through context instead of prop drilling, keeping the public API declarative.
  2. 2A Set in state cleanly models which items are open and toggles between single- and multi-open modes.
  3. 3Deriving aria-expanded and aria-controls from the same state keeps the UI and accessibility tree in sync.

Related explainers

javascript 
function evaluate(expression) {
  const tokens = tokenize(expression);
  let pos = 0;
 

Building a recursive descent calculator

parsing recursion operator-precedence
Intermediate 8 steps
typescript 
import { Injectable, effect, signal, computed } from '@angular/core';
 
interface Preferences {
  theme: 'light' | 'dark';

A signal-based preferences store in Angular

signals state-management persistence
Intermediate 7 steps
javascript 
import { useState, useEffect, useCallback, useRef } from 'react';
 
const cache = new Map();
const inflight = new Map();

Building a stale-while-revalidate hook in React

caching request-deduplication custom-hooks
Advanced 10 steps
typescript 
import { useEffect, useState } from "react";
 
interface Section {
  id: string;

Building a scroll-spy hook in React

custom-hooks intersectionobserver dom-observation
Intermediate 8 steps
javascript 
import { useEffect, useRef, useState } from 'react';
 
export function useDelayedFlag(active, delay = 300) {
  const [visible, setVisible] = useState(false);

Delaying a loading spinner with a React hook

custom-hooks debouncing cleanup
Intermediate 8 steps
javascript 
const SWIPE_THRESHOLD = 80;
const MAX_TRANSLATE = 120;
 
export function attachSwipeToDismiss(element, onDismiss) {

Building a swipe-to-dismiss gesture in JS

touch-events gesture-detection dom-manipulation
Intermediate 10 steps

Share this explainer

Here's the card — post it anywhere.

Building a compound Accordion in React — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code