For example I have some_website/a.json which contains:
{"test":"1","test2":"2"}
and some_website/b.json which contains:
{"test":"3","test2":"4"}
how i can GET and PUT this values in some_website/c.json using XMLHttpRequest like
{"testing1":{"test":"1","test2":"2"},"testing2":{"test":"3","test2":"4"}}
This is not natively possible. There are techniques like “Batch Requests”. Facebook implemented them in their API, for example. Facebook Batch Request