Vanilla JavaScript JWT Auth

Implement JWT authentication in vanilla JavaScript with token storage in localStorage, automatic token attachment to fetch requests, expiry checking, and.

Javascript Auth Jwt Updated: 2026-01-15

Code

snippet

const TOKEN_KEY = 'auth_token';

export const auth = {
  getToken: () => localStorage.getItem(TOKEN_KEY),
  setToken: (t) => localStorage.setItem(TOKEN_KEY, t),
  clear: () => localStorage.removeItem(TOKEN_KEY),
  isExpired: (t) => {
    const payload = JSON.parse(atob(t.split('.')[1]));
    return Date.now() >= payload.exp * 1000;
  },
  fetchWithAuth: async (url, opts = {}) => {
    const token = auth.getToken();
    const res = await fetch(url, {
      ...opts,
      headers: { ...opts.headers, Authorization: `Bearer ${token}` },
    });
    if (res.status === 401) location.href = '/login';
    return res;
  },
};