There are more advantages than just not having to learn something new. There are really compelling reasons you might want to use the same code in some combinati

There are more advantages than just not having to learn something new. There are really compelling reasons you might want to use the same code in some combination of: a web browser, web server, Windows app, Mac app, iOS app, and Android app. For instance, when FB used React Native for building one of their ad manager apps, they had 87% code reuse between iOS and Android (https://twitter.com/brindelle/status/618114397098102785 https://twitter.com/brindelle/status/618114397098102785) The implications that has on a company's eng organization are huge. Another example is the code sharing between client and server in Meteor. That has big implications too. The main reason Javascript is winning as the lingua franca is that it's pretty much the only language you can use in a browser. The main alternatives are things that compile to JS, like Babel, TypeScript, and for a while Coffeescript and Dart were gaining traction too. If browsers could run, say, Python, I suspect you'd see more Python used in this way as well.