Javascript and HTML problem with <a href=""> and Save As... window browser

[K.]

Hello!

I have a problem with A HREF section, which I cannot find in internet.

I have a form, which after submitting creates me a txt file in PHP language.
The file has txt extension.

I would like to run a javascript code which runs after submit form. Then I
would like to run a save browser
window (Save As.....) for this txt file I have just created during
submitting a form.

Header() function in PHP doesn`t suit me, because it opens a html page with
the content of this txt file, and
I would like to have the same window as I would open <a
href="packaged_file.zip">package file</a> that is
I would like to run a Save As... window for this txt file.

Moreover, could you tell me how to write a code for link a
href="file.txt">text file</a> not to open a page with a content of
this file.txt, but to open a Save As.... window browser for this file.txt
file.

Thank you in advance for help
Marcin from Poland