javascript 32 lines · 6 steps

A React hook backed by the URL hash

useHashState mirrors a piece of state into the URL fragment so it survives reloads and stays shareable.

Explained by highlit

React Intermediate custom-hooks url-state event-listeners history-api state-sync

1function useHashState(key, defaultValue) {
const parse = () => {
  const params = new URLSearchParams(window.location.hash.slice(1));
  return params.has(key) ? params.get(key) : defaultValue;
};
6 
const [value, setValue] = React.useState(parse);
8 
React.useEffect(() => {
  const onHashChange = () => setValue(parse());
  window.addEventListener('hashchange', onHashChange);
  return () => window.removeEventListener('hashchange', onHashChange);
}, [key]);
14 
const update = React.useCallback(
  (next) => {
    const params = new URLSearchParams(window.location.hash.slice(1));
    if (next === defaultValue || next == null || next === '') {
      params.delete(key);
    } else {
      params.set(key, next);
    }
    const hash = params.toString();
    const url = hash ? `#${hash}` : window.location.pathname + window.location.search;
    window.history.replaceState(null, '', url);
    setValue(next ?? defaultValue);
  },
  [key, defaultValue]
);
30 
return [value, update];
32}

01 / 01

STEP 01

Walkthrough

Space play ←→ step click any line

Three takeaways

1The URL hash can act as a persistent, shareable store for lightweight UI state.
2Syncing external state into React means listening for its change events and cleaning the listener up.
3Removing a key when its value is the default keeps URLs clean rather than littered with defaults.

Related explainers

javascript

const ROLE_PERMISSIONS = {
  admin: ['users:read', 'users:write', 'billing:read', 'billing:write'],
  manager: ['users:read', 'billing:read'],
  member: ['users:read'],

Role-based permissions middleware in Express

authorization middleware rbac

Intermediate 9 steps

javascript

function attachThousandSeparators(input, { locale = 'en-US' } = {}) {
  const formatter = new Intl.NumberFormat(locale);
  const groupSep = formatter.format(11111).replace(/\d/g, '')[0] || ',';
  const decimalSep = formatter.format(1.1).replace(/\d/g, '')[0] || '.';

Live thousand separators without losing the caret

dom intl caret-preservation

Advanced 8 steps

javascript

import { useReducer, useEffect } from "react";
 
const initialState = { status: "idle", data: null, error: null };

Building a data-fetching hook in React

custom-hooks usereducer data-fetching

Intermediate 9 steps

javascript

const express = require('express');
const app = express();
 
app.get('/health', (req, res) => res.json({ status: 'ok' }));

Graceful shutdown in an Express server

graceful-shutdown signal-handling connection-tracking

Advanced 9 steps

javascript

import { useState, useEffect, useCallback } from 'react';
 
function getColumnCount(width) {
  if (width < 640) return 1;

A responsive column hook in React

custom-hooks debouncing responsive-design

Intermediate 7 steps

javascript

function initCharacterCounter(textarea, options = {}) {
  const maxLength = options.maxLength ?? 280;
  const warnThreshold = options.warnThreshold ?? 0.9;