But that was something that had to be installed on the system

That was only initially true, by the end of its life it was a default component in some major browsers. Such as chrome and internet explorer.

And prior to that it frequently came preinstalled by the manufacturer.

But with all that said, I suspect we’ve missed the intent of the previous comment. To illustrate that none of the alternative means to run code in a web browser has worked out.

And with that said due to market momentum (like how so many apps are electron based) I would expect JavaScript to outlive C++ haha.