BlobBuilder is obsolete, use Blob constructor instead:
URL.createObjectURL(new Blob([/*whatever content*/] , {type:'text/plain'}));
This returns a blob URL which you can then use in an anchor’s href. You can also modify an anchor’s download attribute to manipulate the file name:
<a href="https://stackoverflow.com/*assign url here*/" id="link" download="whatever.txt">download me</a>
Fiddled. If I recall correctly, there are arbitrary restrictions on trusted non-user initiated downloads; thus we’ll stick with a link clicking which is seen as sufficiently user-initiated 🙂
Update: it’s actually pretty trivial to save current document’s html! Whenever our interactive link is clicked, we’ll update its href with a relevant blob. After executing the click-bound event, that’s the download URL that will be navigated to!
$('#link').on('click', function(e){
this.href = URL.createObjectURL(
new Blob([document.documentElement.outerHTML] , {type:'text/html'})
);
});