Rails spinoffs - Oct 2007 - prototype: access to instance properties w/in iterator function

Hello All,

I''m a little confused about how I can access instance properties w/in
an
iterator function.
      function Person(lastName, firstName) {
         this.lastName = lastName;
         this.firstName = firstName;
         this.roles = new Array();
         $w(''developer manager'').each(function(i) {
            //ERROR - "this.roles has no properties"
            this.roles.push(i)
         });
      }


Can someone help me w/ this?

Thanks!

-- john

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On Oct 5, 5:15 am, John Cartwright
<john.c.cartwri...-Wuw85uim5zDR7s880joybQ@public.gmane.org>
wrote:
> Hello All,
>
> I''m a little confused about how I can access instance properties
w/in an
> iterator function.
>       function Person(lastName, firstName) {
>          this.lastName = lastName;
>          this.firstName = firstName;
>          this.roles = new Array();
    var foo = this;

>          $w(''developer manager'').each(function(i) {
To save a needless call to $w() consider:

    [''developer'',
''manager''].each(function(i) {

or even:

  this.roles = [''developer'', ''manager''];

and save yourself some grief ... but for the sake of the exercise
let''s keep going. :-)
>             //ERROR - "this.roles has no properties"
>             this.roles.push(i)
    foo.roles.push(i);

>          });
>       }
Why? The anonymous function passed to the each method as access to all
the variables of the "outer" Person function.  However, each function
object has its own this keyword that (usually) references the object
that it is called as a method of.  If it isn''t a method of some
object, its this keyword will reference the window object.

The anonymous function is called directly, not as say Person.foo, so
its this keyword will reference the global object.

So before calling the function, create a local Person variable that
references whatever this references (the new Person object if it''s
been called as a constructor) so that the anonymous function has
access to the right object.


--
Rob


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$w(''developer manager'').each(function(i) {
             this.roles.push(i)
          }.bind(this));  // <-- Add bind call (old way, still works)

OR

          $w(''developer manager'').each(function(i) {
             this.roles.push(i)
          }, this);  // <-- Pass context parameter (new way, requires  
recent vers of Prototype)

TAG

On Oct 4, 2007, at 1:15 PM, John Cartwright wrote:
>
> Hello All,
>
> I''m a little confused about how I can access instance properties
w/
> in an
> iterator function.
>       function Person(lastName, firstName) {
>          this.lastName = lastName;
>          this.firstName = firstName;
>          this.roles = new Array();
>          $w(''developer manager'').each(function(i) {
>             //ERROR - "this.roles has no properties"
>             this.roles.push(i)
>          });
>       }
>
>
> Can someone help me w/ this?
>
> Thanks!
>
> -- john
>
> >

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I''m not sure what you are trying to do here... but wouldn''t
this
work ?

function Person(lastName, firstName) {
  this.lastName = lastName;
  this.firstName = firstName;
  this.roles = $w(''developer manager'');
}


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Perfect!

I realize the example was a little contrived, but  your explanation  
made perfect sense.

Thanks for the prompt response.

--john


On Oct 4, 2007, at 3:28 PM, RobG wrote:
>
>
>
> On Oct 5, 5:15 am, John Cartwright
<john.c.cartwri...-Wuw85uim5zDR7s880joybQ@public.gmane.org>
> wrote:
>> Hello All,
>>
>> I''m a little confused about how I can access instance
properties w/
>> in an
>> iterator function.
>>       function Person(lastName, firstName) {
>>          this.lastName = lastName;
>>          this.firstName = firstName;
>>          this.roles = new Array();
>
>     var foo = this;
>
>
>>          $w(''developer manager'').each(function(i) {
>
> To save a needless call to $w() consider:
>
>     [''developer'',
''manager''].each(function(i) {
>
> or even:
>
>   this.roles = [''developer'',
''manager''];
>
> and save yourself some grief ... but for the sake of the exercise
> let''s keep going. :-)
>
>>             //ERROR - "this.roles has no properties"
>>             this.roles.push(i)
>
>     foo.roles.push(i);
>
>
>>          });
>>       }
>
> Why? The anonymous function passed to the each method as access to all
> the variables of the "outer" Person function.  However, each
function
> object has its own this keyword that (usually) references the object
> that it is called as a method of.  If it isn''t a method of some
> object, its this keyword will reference the window object.
>
> The anonymous function is called directly, not as say Person.foo, so
> its this keyword will reference the global object.
>
> So before calling the function, create a local Person variable that
> references whatever this references (the new Person object if it''s
> been called as a constructor) so that the anonymous function has
> access to the right object.
>
>
> --
> Rob
>
>
> >

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Very cool! -  Thanks for your help.

--john


On Oct 4, 2007, at 3:49 PM, Tom Gregory wrote:
>
>           $w(''developer manager'').each(function(i) {
>              this.roles.push(i)
>           }.bind(this));  // <-- Add bind call (old way, still works)
>
> OR
>
>           $w(''developer manager'').each(function(i) {
>              this.roles.push(i)
>           }, this);  // <-- Pass context parameter (new way, requires
> recent vers of Prototype)
>
> TAG
>
> On Oct 4, 2007, at 1:15 PM, John Cartwright wrote:
>
>>
>> Hello All,
>>
>> I''m a little confused about how I can access instance
properties w/
>> in an
>> iterator function.
>>       function Person(lastName, firstName) {
>>          this.lastName = lastName;
>>          this.firstName = firstName;
>>          this.roles = new Array();
>>          $w(''developer manager'').each(function(i) {
>>             //ERROR - "this.roles has no properties"
>>             this.roles.push(i)
>>          });
>>       }
>>
>>
>> Can someone help me w/ this?
>>
>> Thanks!
>>
>> -- john
>>
>>>
>
>
> >

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