Useful for updating the vti_indexedpropertykeys property bag item in SharePoint Online, where the key name required is the Base64 encoded Unicode bytes of the property key name

Convert Javascript Text to Unicode Base64 Encoded String.ts

// ==============================================
// ENCODE

/** NODEJS */
const encodedKeyName = Buffer.from("PropertyKeyName", 'utf16le').toString('base64');

/** BROWSER */
function encodeToUtf16LE(str: string): Uint8Array {
  const buffer = new ArrayBuffer(str.length * 2);
  const view = new Uint16Array(buffer);
  for (let i = 0; i < str.length; i++) {
    view[i] = str.charCodeAt(i);
  }
  return new Uint8Array(buffer);
}

/** replace _x005f in key names with "" */
keyBytes = encodeToUtf16LE("PropertyKeyName");
encodedKeyName = btoa(String.fromCharCode(...keyBytes));

// ==============================================
// DECODE

/** NODEJS */
const text = Buffer.from(base64String, 'base64').toString('utf16le');

/** BROWSER */
const text = new TextDecoder('utf-16le').decode(
  new Uint8Array([...atob(base64String)].map(c => c.charCodeAt(0)))
);