On: How necessary are var, let, and const?

[riffraff]

> You can see every single rebinding of a variable within the lexical scope of the function,

I do not think that is true, a called function can side effect the caller environment via `arguments` if that is passed around.

[braythwayt → riffraff]

My understanding is that arguments caller has been removed, and Function.prototype.caller is non-standard:

  > The obsolete `arguments.caller` property used to provide the
  > function that invoked the currently executing function. This
  > property has been removed and no longer works.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

Can you provide an example of modifying a declared variable in a calling environment? I'm very interested!

[riffraff → braythwayt]

I meant this:

    function sidEffecting(ary) {
      ary[0] = ary[2];
    }
    function bar(a,b,c) {
      c = 10
      sidEffecting(arguments);
      return a + b + c;
    }
    bar(1,1,1) // I expect 12, but is 21

I now realize this could actually be not allowed anymore in recent ES, I am not sure, but copy & paste in chrome console still prints 21.