Hey!!
the statement "<script type="text/javascript" src="https://www.test.com?parem=TEST_PARAM"></script>"will not return anything, but just load the script code of the url which you mention in "src" into your
html - if that is a script file.
In your case, "https://www.test.com?parem=TEST_PARAM" seems a web api, so using ajax or xmlhttprequest you can call that url with a parameter and get the result and finally populate fields of your form.