Decode a JSON Web Token in the browser.

decode-jwt.js

function decode(token) {
  const [, payload] = token.split('.')
  try { return JSON.parse(atob(payload)) } catch (err) {}
  const unsafe = payload.replace(/-/g, '+').replace(/_/g, '/')
  let padded = unsafe + '='.repeat(4 - unsafe.length % 4)
  const uriComponent = atob(padded).replace(/(.)/g, (_, c) => {
    const hex = c.charCodeAt(0).toString(16).toUpperCase()
    return '%' + (hex.length < 2 ? '0' : '') + hex
  })
  return JSON.parse(decodeURIComponent(uriComponent))
}