I am new to jsonp and I understand that JSONP is a technique which creates a dynamic
<script src="..."> tag, that wraps the returned JavaScript (or JSON object) with a callback function.
But if I am not mistaken, src attribute in a script tag will hold back all further executions until the script loads, so how can it be asynchronous call?
This related question should shed some light on your question.
Script nodes added dynamically using javascript are executed asynchronously and they won’t block execution of other scripts.