Problem with Access-Control-Allow?

Question

JavaScript

When I get a json object from another server that I gave access to by including Access-Control-Allow-Headers, Access-Control-Allow-Methods and Access-Control-Allow-Origin, and when deserializing the json into a js object , I get a SyntaxError: Unexpected end of JSON input, since the server first responds with Access headers, calls the function to deserialize json, passes undefined there, and only then the request continues and I get a json object, successfully deserialize it in js, can someone know how to avoid an error?