There is no definitive answer to this question, since it is more related to each person’s opinion.
There goes my.
Despite other languages such as Typescript (Microsoft), Dart (Google) and Coffee Script, most browsers only support Javascript.
The Microsoft initiative with the Typescript language is kind of interesting, since the "compiler" (is more a translator than a compiler) generates Javascript code, and therefore can be executed in any browser. The Typescript language, thus, is a super set of JS.
I have never dealt with any of them, and therefore I can’t tell their specific advantages, with the exception of the fact of Typescript compatibility.
Today, what I have done, is to use frameworks to develop client code, since there is no escape from JS.
The best I adapted (although I’m using it for a short time) is Angularjs. It is simple, the documentation is extensive (but not complete), it is possible to integrate it with several other libraries (such as Bootstrap and jQuery) and create very cool things, which favor too much reusability of code.
I also really liked Google Closure, but it is more complicated and requires much more from the developer than Angularjs.
Anyway, in my experience, do not run away from Javascript (at least not yet...), and make use of Frameworks whenever possible.
http://answall.com/questions/4872/como-usar-outra-linguagem-que-n%C3%A3o-javascript-no-browser
– Édipo Costa Rebouças