Which JS function-declaration syntax is correct according to the standard?

Question

  var foo = function(){ return 1; };
  if (true) {
    function foo(){ return 2; }
  }
  foo(); // 1 in Chrome // 2 in FF
  //I just want to be sure, is FF 4 not \"s         


        

Answer 1

The code in the question is not actually allowed at all by current ECMAScript syntax (as of ECMAScript 5). You can do var foo = function() {} inside a block, but you can only do function foo() {} at the toplevel in functions or scripts.

Currently browsers support the code in the question in incompatible ways because they're all implementing extensions to the core language and they implement different extensions. A fully conforming ECMAScript 5 implementation would actually end up with a SyntaxError when compiling this script.

There are proposals to add the ability to do this sort of thing to ECMAScript, but they're not quite finalized yet.