I can only give you anecdotal evidence. In the early 2000s, the U.S. joint military used Smalltalk to write a million-line battle simulator called JWARS. It actually outperformed a similar simulator written in C++ by the U.S. Air Force. I received this information from one of the chief JWARS architects.

Around the turn of the millennium, JP Morgan wrote a massive financial risk management system called Kapital…in Smalltalk.

Around the same time period, Orient Overseas Container Lines used Smalltalk to write a globe-spanning shipping management software called IRIS-2.

Correct me if I’m wrong, but there is yet to be a JavaScript application or system on this scale. If there is, I’d very much like to know what it is.