Hi,
> is there a way that I can get rid of all these usages of "this"
No. `this` is different in Javascript than in some other languages
with the same keyword, in several ways. One of these is that
unqualified references like your _div (without anything in front of
it) are not automatically resolved against property names on `this`;
all identifier resolution in Javascript is lexically-based, using the
concept of a "scope chain" (more below if you're interested). So you
have to explicitly type `this.` when accessing the properties on
`this` (just as you have to type `foo.` to access the properties on
`foo`), or as you've found, you can use `with`. Be aware that using
`with` has some "gotchas" that are not obvious. Douglas Crockford
lists many of these in his "with Statement Considered Harmful"[1]
article (I'm not a fan of "Considered Harmful" articles[2], but
Crockford lays out the issues fairly well). My point isn't "don't use
it", it's "be sure you understand the gotchas when using it".
About the scope chain and identifier resolution: One of the things I
love about Javascript is that basically *everything* is an object,
even if some of the objects are hidden behind the scenes. One of these
behind-the-scenes objects is the "variable object" (the "binding
object of the variable environment" in the latest spec -- yikes). When
you declare a variable using `var`, you're adding a *property* to the
variable object for the current scope. The variable object has
properties for all `var`s, all functions declared in the scope, and
(if the scope relates to a function) all named arguments to the
function. When the step-by-step code within the scope is executing,
that scope's variable object is at the beginning of the "scope chain."
All unqualified references are first checked against that variable
object to see if they match a property on it. If they do, that
property is used; if not, the next variable object in the chain is
checked; etc.
Example:
var x = 1;
function foo() {
var y = 2;
function bar() {
var z = 3;
alert(x);
alert(y);
alert(z);
}
}
We have three "scopes" there: Global scope, `foo`'s scope, and `bar`'s
scope. Consequently, we have three variable objects. When code within
`bar` is being executed, the scope chain consists of `bar`'s variable
object, followed by `foo`'s, followed by the global variable object.
When `bar` references `z`, the `z` property is found on the first
variable object and used. When `bar` references `y`, it's not on the
first variable object but it is on the second one, so it's used from
there. Accessing `x` involves going back two variable objects to the
global one.
As you can see, `this` doesn't come into it -- it's nowhere on the
scope chain unless you insert it, which is exactly what `with` does:
Puts the object you specify at the beginning of the scope chain.
Now, I called the variable object a behind-the-scenes object. That's
usually true, but there's an exception: The variable object for the
global scope is the global object, which on browsers is `window` (more
accurately, on browsers the global object has a property, `window`, it
points to itself with). That's why when you declare variables and
functions at global scope, they magically show up as properties on
`window`.
[1] http://yuiblog.com/blog/2006/04/11/with-statement-considered-harmful/
[2] http://meyerweb.com/eric/comment/chech.html
HTH,
--
T.J. Crowder
Independent Software Consultant
tj / crowder software / com
www.crowdersoftware.com
On Apr 29, 9:17 am, Ran Berenfeld <berenfeld...@gmail.com> wrote:
> Hi all
> I have written a class using prototype Class object
> and after playing it for a while, I saw that I need to use the "with"
> keyword in the class members,
> so I can access its members
>
> here is the relevant part of the class : (the member is "_div")
>
> var JSClass = Class.create ({
> initialize: function(initParams) {
>
> if (initParams.div)
> {
> *this*._div = $(initParams.div);
> }
> else
> {
> *this*._div = new Element(div);
> }
> },
> // an example of a member function
> setComment: function(msg)
> {
> *with(this)*
> * {*
> * *_div.innerHTML = msg;
> * }*
> }
>
> });
>
> is there a way that I can get rid of all these usages of "this"
>
> Thanks
> Ran
>
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