JavaScript is like Gravity on the client side, and with ES6/7 it's about to become a much nicer language too. You could never run Ruby natively, in a widespread

JavaScript is like Gravity on the client side, and with ES6/7 it's about to become a much nicer language too. You could never run Ruby natively, in a widespread manner, on the browser. With one language you can now build a complete stack and target all devices. That's quite big.