The JavaScript x () function {..} is considered as var x = function () {..} inside the `if 'in Firefox, and not in Chrome and Opera

Question

Consider the following JavaScript code:

(function(){
  foo();
  function foo(){ alert('Hello, World!'); }
})();

In Firefox, Opera, and Chrome, this behaves as expected; we get a warning. Now in contrast:

(function(){
  if (true){
    foo();
    function foo(){ alert('Hello, World!'); }
  }
})();

Firefox 3.6 and 4 (beta) (i.e. SpiderMonkey for both) throws an exception: foo is undefined

Chrome (i.e.V8) and Opera (i.e. any Opera engine) work as expected (for me).

What is the right behavior, or is it left for implementation to solve?

FWIW, re-enable it in the function, and again it's good to return to FF:

(function(){
  if (true){
    (function(){
      foo();
      function foo(){ alert('Hello, World!'); }
    })();
  }
})();

+3

Christopher done Mar 07 '11 at 8:44

4 answers

, symantec. . foo, . .

+1

hungryMind 07 . '11 8:51

foo , if. if . , , Chrome .. , FF , .

, - .

+1

Tyler 07 . '11 8:58

, :

var foo = function() {alert ('Hello, World!'); } Foo();

inside (function () {}) () you will get true private methods.

0

Kir Mar 07 '11 at 9:08

Christopher Done · Accepted Answer · 2011-03-07T10:00:58+0000

According to the ECMA-262 5th Edition specification , it SourceElementis defined as:

SourceElement :
Statement 
FunctionDeclaration

, FunctionDeclaration Statement . (, if) Statement s:

Block :
   { StatementList opt }

StatementList :
   Statement
   StatementList  Statement

FunctionStatement:

try {
  function Fze(b,a){return b.unselectable=a}
  /*...*/
} catch(e) { _DumpException(e) }

FunctionExpression:

var Fze;
try {
  Fze = function(b,a){return b.unselectable=a};
  /*...*/
} catch(e) { _DumpException(e) }

FunctionDeclaration:

function aa(b,a){return b.unselectable=a}