It’s important to intentionally declare your variables within a specific scope, using var, to keep your code clear and maintainable.
Why? Var is an old way of declaring variables. let and const. A Gentle Introduction to ES6.
While this assumption might be partially true, it's still possible that some of these features remain a mystery to some devs. A lot of shiny new features came out with ES2015 (ES6). This will update the value of greeting.message without returning errors.. Hoisting of const.