You need a tool like this to monitor run-time browser errors. When browsers support a language that catches 100% of errors at compile time then you won't need tools like this.

But I see what you're saying. Except for the declarative style popularized by React and also implemented in Mithril, Preact and Inferno, and except for the rise in popularity of TypeScript, and except for a lot of attention paid lately to immutable data structures, and except for jslint being created in 2002 and lots of similar tools since then, and except for the wide variety of JavaScript-based unit test frameworks, it really seems like the JavaScript community has no clue that there are ways to prevent the errors you describe and no inclination to prevent them.