I've gotten pretty far with Mithril and polyfills (mainly for JSON support) targetting IE7. If you're worried about backwards compatibility, then jQuery is the

I've gotten pretty far with Mithril and polyfills (mainly for JSON support) targetting IE7. If you're worried about backwards compatibility, then jQuery is the right tool; however, if less than 2% of your users are using an unsupported version of Internet Explorer, I would spend more time flashing a message instructing these users to upgrade.