[Renaud]

Wouldn't TypeScript help a lot in handling these changes?

You break/change something and then the rest of your code wouldn't compile until you fixed it everywhere (and it would show you where). You wouldn't have to worry whether you forgot something since the compiler wouldn't let you get away with it. Refactoring tools on top of TypeScript (like Resharper and Coderush) will eventually be able to safely do these changes quickly across the whole project.

[epidemian]

But it's cumbersome to have to change lots of code just because a property of some object became computed instead of directly stored (or vice versa). And it's unfeasible to do so if you're developing a library (for external usage, or internal usage within a company)... you can't just go and fix all the code that used it.