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Re: Can somebody explain this to me

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Christoph M. Becker wrote:

> John Harris wrote:
>> On Wed, 07 Jan 2015 17:22:40 +0100, Thomas 'PointedEars' Lahn
>> <PointedEars@web.de> wrote:
>>> It is because, as is obvious from the above, he has not realized yet
>>> that there are (at least) two ways to “define” a function in ECMAScript,
>>> of which one includes a *declaration*.
>> 
>> Both ways create a function object. One way gives it a global name,
>> the other need not. What else matters?
> 
> Most importantly scope rules.

The scope (chain) rules are the same with either syntax.

> A function declaration creates a function object that is passed in the 
> *variable* environment of the running execution context as environment;
> a function object that is created by a function expression is passed in 
> the *lexical* environment.

Objects are not "passed in environments".

<http://ecma-international.org/ecma-262/5.1/#sec-10.3>

| LexicalEnvironment  | Identifies the Lexical Environment
|                     | used to resolve identifier references made by code
|                     | within this execution context.
| --------------------+---------------------------------------------------
| VariableEnvironment | Identifies the Lexical Environment
|                     | whose environment record holds bindings created by
|                     | VariableStatements and FunctionDeclarations within 
|                     | this execution context.

(intentional word-wrap)

> Informally, one might say that function declarations are "hoisted".

Yes, but as with all informal descriptions, it is imprecise and potentially 
misleading.  For example, a so "hoisted" function can still access 
identifiers in the outer execution context even though they have only been 
defined (and assigned to) later, because it is a closure and because of the 
scope chain:

  var answer;

  function deepThought ()
  {
    return answer;
  }

  /* undefined */
  deepThought();

  answer = 42;

  /* 42 */
  deepThought();

> Another pitfall that one should be aware of is that the behavior of a
> function expression in a statement context is standardized, while the
> behavior of a function declaration (better called function statement
> here) in a statement context is not, even though it is allowed in
> several ECMAScript implementations.

True.  However, I think it is more important to realize that function 
expressions observe source code order (so I referred to that).  A function 
defined with a function expression is not defined before execution *passed* 
the latter.

  /* 42 */
  foo();

  function foo ()
  {
    return 42;
  }

  /* TypeError: undefined is not a function */
  bar();

  var bar = function () {
    return 42;
  };

[Per Specification, this is independent of whether the function *expression* 
contains an identifier (a function *declaration* must contain an identifier 
or it is parsed as a function expression).  There is a JScript bug, fixed in 
version 9+ when in IE 9+ standards Document Mode¹ (test with Firebug Lite or 
F12 – developer tools), that allows the bar() call above to be successful if 
you write

  var bar = function bar () {
    return 42;
  }; 

instead.  IOW, the function identifier can leak to the outer scope.

______
¹ Did I already say that there is no javascript/Javascript?]

-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | SVN: <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | ES Matrix: <http://PointedEars.de/es-matrix>
Please do not cc me. / Bitte keine Kopien per E-Mail.

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Can somebody explain this to me "Tony Johansson" <johansson.andersson@telia.com> - 2015-01-06 00:48 +0100
  Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-06 01:40 +0100
    Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-06 16:01 +0000
      Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-06 17:26 +0100
        Re: Can somebody explain this to me Joao Rodrigues <groups_jr-1@yahoo.com> - 2015-01-07 00:45 -0200
          Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-07 04:35 +0100
            Re: Can somebody explain this to me Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2015-01-07 16:15 -0200
              Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-07 21:20 +0100
                Re: Can somebody explain this to me "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-01-08 00:00 +0100
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-08 00:09 +0100
                Re: Can somebody explain this to me "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-01-08 10:53 +0100
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-08 16:17 +0100
                Re: Can somebody explain this to me "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-01-08 17:04 +0100
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-08 19:02 +0100
        Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-07 15:37 +0000
          Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-07 17:01 +0100
            Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-08 10:43 +0000
              Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-08 13:16 +0100
          Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-08 16:43 +0100
            Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-09 20:16 +0000
              Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-09 22:11 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-10 16:58 +0000
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-11 12:41 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-12 15:46 +0000
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-12 18:01 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-13 10:38 +0000
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-14 16:06 +0000
              Re: Can somebody explain this to me Scott Sauyet <scott.sauyet@gmail.com> - 2015-01-21 13:00 -0800
                Re: Can somebody explain this to me Joao Rodrigues <groups_jr-1@yahoo.com> - 2015-01-21 20:53 -0200
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-22 11:43 +0000
                Re: Can somebody explain this to me Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2015-01-22 10:20 -0200
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-23 19:42 +0000
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-28 18:14 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-22 11:39 +0000
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-22 13:27 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-23 14:36 +0000
                Re: Can somebody explain this to me Scott Sauyet <scott.sauyet@gmail.com> - 2015-01-23 08:51 -0800
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-23 23:17 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-24 16:42 +0000
                Re: Can somebody explain this to me Scott Sauyet <scott.sauyet@gmail.com> - 2015-01-24 15:35 -0800
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-25 11:08 +0000
                Re: Can somebody explain this to me "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2015-01-26 08:33 -0800
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-27 14:10 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-28 15:50 +0000
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-28 18:26 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-29 10:29 +0000
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-31 00:37 +0100
                Re: Can somebody explain this to me "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2015-01-28 13:30 -0800
                Re: Can somebody explain this to me "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-01-28 22:40 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-29 10:32 +0000
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-29 10:23 +0000
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-29 11:04 +0000
                Re: Can somebody explain this to me "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2015-01-26 08:21 -0800
                Re: Can somebody explain this to me Scott Sauyet <scott.sauyet@gmail.com> - 2015-01-26 11:10 -0800
                Re: Can somebody explain this to me Scott Sauyet <scott.sauyet@gmail.com> - 2015-01-22 06:36 -0800
      Re: Can somebody explain this to me Tim Streater <timstreater@greenbee.net> - 2015-01-06 17:34 +0000
        Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-06 19:03 +0100
          Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-07 15:07 +0000
            Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-07 16:41 +0100
              Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-07 17:22 +0100
                Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-08 10:36 +0000
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-08 13:36 +0100
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-08 17:54 +0100
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-08 19:48 +0100
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-08 22:09 +0100
                Re: Can somebody explain this to me Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2015-01-08 18:22 -0200
                Re: Can somebody explain this to me "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-01-08 22:13 +0100
                Re: Can somebody explain this to me Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-01-08 22:25 +0100
              Re: Can somebody explain this to me John Harris <niam@jghnorth.org.uk.invalid> - 2015-01-08 10:25 +0000
                Re: Can somebody explain this to me "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-01-08 11:33 +0100

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