Comment by just_astounded

There are a lot of reasons, honestly, and it's great beer conversation, but from a high level: producing a concrete instance that invokes a constructor function with a shiny pristine 'this' to build on is a pretty great pattern. Add the ability to muck about with clever prototype manipulation, and you have pretty enormous power - you can do everything that classic OOP can do (if that's your thing) and a lot more.