I tend to disagree. As of today, Javascript is the least common denominator of all the advanced web technologies. If you know JS fairly well, you're able to understand nearly everything under the hood if you want to.
If you have CLR/JVM in addition, this just brings more problems to the table, especially when you have to deal with much more languages which do not "compile" to JS or when you have to deal with proprietary APIs/Libraries.
At the end of the day, "what can be written in Javascript will be written in Javascript", thus whatever functionality you want from other technology stacks will be available sooner or later, and is usable from your preferred "compiles to JS" language of choice. If you want a neat debugger, try Typescript maybe? If you like to think functional, give Livescript a shot. Only want class-based OOP and a fairly expressive syntax? Then just use Coffeescript. Or just use Javascript as is if you like it. When you need more performance, check out ASM.js if it fits.
Thanks to Emscripten you may even use languages like C++ for your web development.
If you have CLR/JVM in addition, this just brings more problems to the table, especially when you have to deal with much more languages which do not "compile" to JS or when you have to deal with proprietary APIs/Libraries.
At the end of the day, "what can be written in Javascript will be written in Javascript", thus whatever functionality you want from other technology stacks will be available sooner or later, and is usable from your preferred "compiles to JS" language of choice. If you want a neat debugger, try Typescript maybe? If you like to think functional, give Livescript a shot. Only want class-based OOP and a fairly expressive syntax? Then just use Coffeescript. Or just use Javascript as is if you like it. When you need more performance, check out ASM.js if it fits.
Thanks to Emscripten you may even use languages like C++ for your web development.