sha256.js

// Source: adapted from https://stackoverflow.com/a/48161723
// This returns a SHA-256-hashed string.
function sha256(message) {
  // Encode as UTF-8.
  const msgBuffer = new TextEncoder('utf-8').encode(message);

  if (typeof window !== 'object' || !window.crypto) {
    return Promise.resolve(null);
  }

  // Hash the message.
  return window.crypto.subtle.digest('SHA-256', msgBuffer).then(hashBuffer => {
    // Convert `ArrayBuffer` to `Array`.
    const hashArray = Array.from(new Uint8Array(hashBuffer));

    // Convert bytes to hex string.
    const hashHex = hashArray.map(b => `00${b.toString(16)}`.slice(-2)).join('');
    return hashHex;
  });
}