No way to do this using javascript. Just specify alternative fonts in CSS.
<style>
body {
font-family: Verdana,Tahoma,Arial;
}
</style>
But if you're using uncommon fonts, then the only viable solution is to provide a download link and have a note in your page. Something like:
This page is best viewed using this font: <img src="verdana.gif" alt="Verdana font" />. If you see the font here different than that of the image, I recommend you to <a href="verdana.ttf">download</a> it and install in your system.