I would suggest using Google's Webfontloader, it's incredibly simple to use:

WebFont.load({

    google: {

        families: ['Droid Sans', 'Droid Serif']

    }

});

Which would allow you to use the massive web font library hosted by google here, without needing to explicitly specify the CSS. You can use custom fonts as well if you're willing to use a style tag or a .css file (or you can inject the @font-face via javascript.) There are other web font providers that work with the Webfontloader, just look on the github page.

If you're interested in learning how to do this manually in javascript, any query on injecting CSS via javascript will sort you, but, that's still technically using CSS. Not sure if this/that is what you want.