On 12/16/10, Balázs Galambosi <[email protected]> wrote:
Learn interleaved reply; do not top post.
[...]
>
> I think Google doesn't use closures for private variables because of
> the small performance penality it has (variables are searched up the
> scope-chain). As far as I know they're utilizing Closure Compiler's
> ability to guard private members (using @private):
>
<touchy>
A more likely explanation is that the authors of Closure COmpiler do
not understand [[Scope]].
</touchy>
> /**
> * A simple private memeber of goog.
> * @private
> * @type {String}
> */
> goog._secret = "cannot be accessed directly from outside";
>
Running that example, comments and all, through CC at:
http://closure-compiler.appspot.com/home
The result is:
| goog._secret="cannot be accessed directly from outside";
Identifier `_secret` can be accessed directly from outside.
Similarly for the example in the article you've linked, which states
about an example:
"The compiler will ensure that the private member _birthDay isn’t read
or write through out the whole application."
When I run that example through CC, I get the output:
function User(){this._birthDay=new
Date}User.prototype.getBirthYear=function(){return
this._birthDay.getYear()};var me=new
User;document.write(me.getBirthYear().toString());
The _birthDay property is not private:
| var u = new User;
| alert(user._birthDay);
The `_birthDay` property is not private at all.
> You can read more about Google CC OOP features at:
> http://calendar.perfplanet.com/2010/coding-better-object-oriented-javascript-with-closure-compiler/
>
Oh boy. HEre we go.
| Only JavaScript Ninjas survive?
|
| So this is why everyone is trying so hard to hire a JavaScript ninja
or become one
|
| However, is it really necessary to write JavaScript like this?
|
| if (!("a" in window)) {
| var a = 1;
| }
| alert(a);
What does he think that does? Realize that if `window` is the global
object (and it is in web browsers), then `a = 1` can never be
evaluated.
Does he explain what that code does? No! He just says its all to
confusing and instead:
"Let Closure Compiler make you a JavaScript Samurai!"
I mentioned javascript library blog FUD yesterday and this is a fine
example. They want to make cross browser scripting seem so scary and
complicated. This stuff is not that hard. This is a tricky example,
here but let me break that down and you may likely have one up on the
author of this article.
Example:
| if (!("a" in window)) {
| var a = 1;
| }
| alert(a);
There are two passes of the code here. First, there is Variable
Instantiation. This is where identifiers with variable statement,
FunctionDeclaration, and parameters (for function code) are added to
the variable object (VO), and given attribute {DontDelete}. The
{DontDelete} attribute means that if you try to delete a variable, it
will fail, e.g.
var a;
var deleted = delete a; // false (except in eval code)
The second pass is evaluation of Statements, such as the IfStatement
or the assigmentExpression `a = 1`.
In Variable Instantiation, `a` is added to the VO, if it does not
already exist, and given value `undefined`. If the VO already has an
`a` property, its value is unchanged.
Next, in evaluation of statements, the IfStatement is evaluated. So
what is `"a" in window"`? result? In a web browser, the global object
its he global variable object is the window. Thus `"a" in window` is
true.
So `"a" in window` is true, and the Logical NOT operator (!) converts
that to false. And:
| if( !("a" in window) )
Must be false!
The result of the program is the creation of a global identifier `a`
with value `undefined` and attributes {DontDelete}. JScript 5.8 and
below, IIRC, add also {DontEnum} (you are not expected to know that
bug).
Instead of explaining what that toy example does, the author goes on
to tell you you need Closure Compiler to be a "Samurai".
Garrett
> - Balázs
>
> 2010/12/16 bawigga <[email protected]>:
>> What is the correct nomenclature for the following ways of writing JS. I
>> understand how each example works, but I don't know how to put the
>> following
>> patterns into words. I also don't know when it's best to use one pattern
>> over the other (perhaps just preference)?
>> I personally prefer ex 2/3 as I feel as though it keeps my code a lot
>> cleaner, and easier to maintain. It would seem ex1 doesn't really help in
>> code maintainability as you still have a bunch of seemingly random
>> unrelated
>> functions within a single namespace.
>> I also found that the google closure lib uses ex 1, and jquery seems to
>> use
>> ex 2/3. Why would they choose one over the other?
>>
>> Google Closure -
>> http://code.google.com/p/closure-library/source/browse/trunk/closure/goog/base.js?r=544
>> - namespace pattern?
>> jQuery - http://code.jquery.com/jquery-1.4.4.js - using object literal?
>>
>> // ex 1 (namespace pattern?)
>> goog.a = function() {
>> //do something
>> };
>> goog.b = function(){
>> //do something
>> };
>> // ex2 (module pattern?)
>> goog = (function(){
>> return {
>> a: function(){
>> // do something
>> },
>> b: function() {
>> // do something
>> }
>> };
>> })();
>> // ex 3 (literal pattern?)
>> goog = {
>> a: function(){
>> // do something
>> },
>> b: function() {
>> // do something
>> }
>> }
>>
>> --
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>>
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>>
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>>
>
> --
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>
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>
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--
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