how to download thing with javascript code example

Example 1: javascript download file

$('a#someID').attr({target: '_blank', 
                    href  : 'http://localhost/directory/file.pdf'});

Example 2: js download file from webserver

<iframe id="download_iframe" style="display:none;"></iframe>
<script>
	document.getElementById('download_iframe').src = "/example/example.txt";
</script>