instanceof operator works as it should.]]>
instanceof operator. One way to do it can be like this:
if(myVariable instanceof myClass) { ... }myVariable is an instance (object) of the class myClass. To create an object (an instance) from a class you use the new operator, e.g: myVariable = new myClass();
The idea behind the instanceof operator is that it provides the possibility to test which class an object originated from, and thereby use only methods and properties you know exist in instances of that class. In other words, you can write a method that does different things depending upon which class it belongs to, which in turn can result in more powerful code that's still easy to maintain.
This is a really good idea, but it's not consistently implemented. As I found out earlier MSIE(Microsoft Internet Explorer) is unable to test objects sent as arguments from another window. The question I sought answered was whether there existed other cases where the tests failed, and if so, which browsers were affected.
I created a testcase that consists of the original problem case (#1) and two variations. The first test calls a function in a (different) window passing a local variable as the argument. As I mentioned earlier this is where MSIE(Microsoft Internet Explorer) fails when the function is in another window. In the test the function is called twice, first a primitive number value (var notNumberClass = 8;) is passed and the test should tell it's not an instance of any of the basic classes. The second time an object created from the Number class is passed (var isNumberClass = new Number(8);) and it should be identified as being an instance of the Number and Object classes (remember that all classes in JavaScript are descendants of the Object class).
The first variation (case #2) tries to turn the problem around by calling a function local to the testcase window/frame while the argument moves around. Again the test is done with both a primitive number value and an instance of the Number class, and the results should be the same as in the first case. I created this second test because I wasn't sure whether the browsers that didn't correctly tackle case #1 would show the same symptoms in the second case. According to my test results the browsers seem to fail in the exact same way in both cases.
The last case (#3) moves both the function and the argument around, but the variable being tested is always local to the window containing the function. None of the browsers I tested had any problems with this test.
I ran the tests with four browsers:
* Microsoft Internet Explorer 6
* Mozilla 1.5
* Opera 7.23
* Konqueror 3.1-15 Red Hat
Mozilla 1.5 is the only browser that doesn't fail on any of the three tests. The other three browsers all get test #3 right, but denies that the object is an instance of the classes Number and Object in test #1 and #2. I've yet to read enough of the ECMA-262 spec to understand why they behave like they do, but as far as I understand the definition of the instanceof operator it's rather surprising that that it shouldn't work across windows/frames.
[Note: This is an English translation of an article I wrote for my Norwegian blog. If you'd prefer the Norwegian version, visit Instanser av klasser, instanceof-operatoren]]]>
From: ********* Title: "JavaScript and Sex" Points: 5 Date: Monday, March 13 2000 - 01:48PM CET Can anyone tell me how I can use my skills in JavaScript to get more girls/sex please. Thanks in advance ****From: nettrom Date: Monday, March 13 2000 - 01:40PM CET Unfortunately the methods needed to get girls/sex in JavaScript are dependant upon the DOM of each girl. Therefore, you will have to make sure you sniff what version of said DOM each girl has before you try to get them. If you do not do this the result is a fatal error. Therefore, always start each session with:
var mySelf = new Me();
var myGirl = new Girl();
if(myGirl.DOMversion < 2) {
myGirl.leave(); // too old DOM version
}if(myGirl.stillPresent) {
// girl is still with us
myGirl.get(); // get girl!
}if(myGirl.stillPresent) {
// girl is still with us
myGirl.get(); // get girl!
mySelf.undress();
myGirl.undress();
sex.safe = true; // must rember to have safe sex!
myGirl.getOnBed();
mySelf.getOnBed();
mySelf.haveSex(myGirl);
}function showCalendar(targetForm, targetDate) {
// code to create HTML for calendar went here
// code that opens and writes the calendar
var calWindow = window.open('', 'calendarWindow', ...);
calWindow.document.write(lotsaHTML);
calWindow.document.close();
}
This code was called by links in the calendar window whenever the user wanted to navigate back/forward a month, and that functionality didn't work. I failed to spot obvious errors in the code and sent off some code being a shot off the hip, but it totally failed to solve the problem.
I then suggested to rewrite the code so that it reused a global window reference whenever it's available. The code became:
var globalWindowRef;
function showCalendar(targetForm, targetDate) {
// code to create HTML for calendar went here
// code that opens and writes the calendar
var calWindow;
if(globalWindowRef && !globalWindowRef.closed) {
calWindow = globalWindowRef;
} else {
calWindow = window.open('', 'calendarWindow', ...);
}
calWindow.document.write(lotsaHTML);
calWindow.document.close();
}(defun pfm-run-command-on-article (command &optional replace)
"Run the full text of the current article through a filter.
The full text of the current article is run through the specified COMMAND
as a filter. The output of the command is returned."
(interactive "sCommand: \nP")
(let ((n (gnus-summary-article-number))
(g gnus-newsgroup-name))
(with-temp-buffer
(gnus-request-article n g (current-buffer))
(shell-command-on-region
(point-min) (point-max)
command)
(if replace
(gnus-request-replace-article n g (current-buffer)))
)))(define-key gnus-summary-mode-map
(read-kbd-macro "C-c R s")
'(lambda () (interactive) (pfm-run-command-on-article "sa-learn --spam --single" ))
)
(define-key gnus-summary-mode-map
(read-kbd-macro "C-c R h")
'(lambda () (interactive) (pfm-run-command-on-article "sa-learn --ham --single"))