Ajax response

Ajax response

Hi Folks,

I am getting this response from server

{"targetRequestUri":"/onePageCheckout","javax.servlet.request.key_size":128,"_CONTEXT_ROOT_":"/home/ankit/ofbiz_dev/jquery/specialpurpose/ecommerce/webapp/ecommerce/","javax.servlet.request.ssl_session":"4ca5f317564be1e1678fefa000004a66f4b99dc225826e28b18dc4a9983c7a90","_CONTROL_PATH_":"/ecommerce/control","javax.servlet.request.cipher_suite":"TLS_DHE_RSA_WITH_AES_128_CBC_SHA","_FORWARDED_FROM_SERVLET_":true,"_SERVER_ROOT_URL_":"https://localhost:8447","thisRequestUri":"json","_ERROR_MESSAGE_":"The promotion code [feds] is not valid."}.

Now i need the value of this

_ERROR_MESSAGE_ only, how can i retrive this value from the response.

Thanks in advance!