title: How can I generate HMAC in React-Native?
body: <p>I need to create HmacSHA256 from a string with a private key...
  I use react-native-crypto-js but I cant use it's HmacSHA256 method,
  it keeps getting me "undefined function" error, here is my code:</p>
  
  <pre><code>const signature = CryptoJS.HmacSHA256('simple', '123456789');
      const signatureBase = signature.toString(CryptoJS.enc.Base64);
  </code></pre>
  
  <p>I followed it's document either but still getting same error,
  if you know another solution or the correct way to use this package please help me.
  thanks.</p>