Although the strange thing is now we have WebAssembly, which really seems like it is the assembly language of the web, at least for resource-intensive software like games. But in the meanwhile, JavaScript’s gone from being a terrible language to (arguably) a perfectly usable one, it’s built up a significant body of shared community expertise, accumulated some excellent tools, and could remain the de facto standard for a long time just based on the inertia of its previous success. (What Replaces JavaScript has a good write up of WebAssembly, if you’re curious.)