Shadows of JavaScript

2017-02-02T18:43:58Z

Months ago, Robbie had found this scoping problem in Python, which I reduced to essentials.

I've started finally learning JavaScript, and it has nicer lambdas than Python, and proper hiding of nested functions unlike Perl. But it has the same scope problem:

g1 = 12;
function func() {
  document.getElementById("demo").innerHTML = g1;

  var g1 = 5;

}
func();

(I'm not including the HTML framework because DW/LJ would yell at me if I did.)

Output is 'undefined', rather than 12. As in Python, the local variable further down shadows the outer scope variable (doesn't matter if the "g1=12" has a 'var' before it) even for lines before the local variable.

As mentioned before, Perl has proper lexical scoping here (though not for nested functions.) I don't think I can even create similar code in Scheme/Lisp, where the scoping is explicit with parentheses. (There's 'define' but I think that makes a new global, and it didn't work.) In Ocaml I have

let g1="10";;

let func () =
  print_endline g1;
  let g1="cat" in
    g1
  ;;

func();;

Which I suspect is as explicit as Lisp parentheses, in its own way; the print line is obviously outside the following "let ... in...".

comments

mysteries of TCO

2016-12-11T20:36:06Z

So I've learned that gcc/g++ do tail call optimization with the -O2 option; supposedly MS Visual Studio and clang do it when they can as well. I have tested this:

( this got long )

comments

Rich and Strange Aeons

Shadows of JavaScript

mysteries of TCO