How to fix this code to choose only text files?

Question

I am running a batch program to pick out the text files from a dialog window, but it's picking all type of files instead.

The batch file I'm running:

    set dialog="about:<input type=file id=FILE><script>FILE.click();new ActiveXObject
    set dialog=%dialog%('Scripting.FileSystemObject').GetStandardStream(1).WriteLine(FILE.value);
    set dialog=%dialog%close();resizeTo(0,0);</script>"

    for /f "tokens=* delims=" %%p in ('mshta.exe %dialog%') do set "file=%%p"
    echo selected  file is : "%file%"
    pause

Expected output:

The pop up file browser must only choose text files *.txt instead all files *.*