September, 2003

JScript and VBScript have completely different garbage collectors. Occasionally people ask me how the garbage collectors work and what the differences are.

...

Every now and then someone will ask me what the VBScript error message "Cannot use parentheses when calling a Sub" means. I always smile when I hear that question. I tell people that the error means that you CANNOT use PARENTHESES when CALLING a SUB -- which word didn't you understand?...

If you've ever done any C++ or C programming that used COM objects, you'll certainly have seen code like this: STDMETHODIMP CFo:Bar(BSTR bstrABC) { // ... What is this BSTR thing, and how does it differ from WCHAR* ? ...

A number of people have pointed out to me over the years that VBScript's Round function is a bit weird. It seems like it should be pretty straightforward -- you pick the integer closest to the number you've got, end of story. But what about, say, 1.5? There are two closest integers. Do you go up or down?...

JScript, as I noted yesterday, is a functional language. That doesn't mean that it works particularly well (though I hope it does) but rather that it treats functions as first-class objects. Functions can be passed around and assigned to variables just as strings or integers can be. A reader commented yesterday that "closures are your friends". Well, actually there are important situations where closures are NOT your friends! Let's talk a bit about those. First off, what's a closure?...

While we're on the subject of semantic differences between seemingly similar syntaxes, let me just take this opportunity to quickly answer a frequently asked question: why doesn't for in enumerate a collection?...

I mentioned Hungarian Notation in my last post -- a topic of ongoing religious controversy amongst COM developers. Some people swear by it, some people swear about it. The anti-Hungarian argument usually goes something like this: "What is the point of...

I've got a few ideas for some future posts that depend on the reader understanding a little bit about COM threading. Since I myself understand only a little bit about COM threading, I'll just do a brain dump for you all right here.

...

Earlier I alluded to the fact that JScript arrays are objects but VBScript arrays are not. What's up with that?...

Joel's law of leaky abstractions rears its ugly head once more. I try to never use smart pointers because... I'm not smart enough....

I suspect that I may be the world's leading authority on bugs having to do with the OLEAUT date format, a dubious distinction at best. ...

Arr! When I was a young swabbie seven years ago I was given the task of implementing the Scripting.Dictionary object, and I didn't yet understand all the stuff I just told you maties about threading. Mayhem followed!

...

Occasionally I get questions from people who are confused over the semantics of data that's not there. Why does VBScript have Null, Nothing and Empty, and what are the differences between them?...

Basically, the rule is pretty simple -- if you want to pass a variable by reference, you've got to pass the variable, period. VBScript does not support passing object properties by reference....

One of our excellent customer support staff in the United Kingdom asked me this morning what "anonymous functions" are in JScript. Well, it's a little complicated. Two things come to mind: realio-trulio anonymous functions, and what we used to call "scriptlets". ...

I said earlier that certificates could be used to establish identity and hence the right to run trustworthy software on your machine. I want to emphasize in the strongest possible terms that this is not all that certificates are used for. A lot of people are confused by this, including a lot of very smart, technically savvy developers. Cryptographic security is complex and poorly understood....

I was talking about reference types vs. by-reference variables a while back. Recall that both JScript and VBScript have reference types (ie, objects) but JScript does not have by-reference variables. COM supports passing variable references around, but unfortunately the intersection of early-bound COM and late-bound IDispatch is a little bit goofy. ...

VBScript version 1.0 was written by one of the VB compiler devs, one of those uber-productive guys who implements compilers on the weekend for fun. It was implemented and tested extremely rapidly, and as a result, a few of the less important methods in the VB runtime were not ported to the VBScript runtime. My first task as a full timer at Microsoft was to add the missing functions to VBScript 2.0...

Security experts often use word pairs such as safe/dangerous, trusted/untrusted, and benign/hostile without clearly distinguishing them from each other. These distinctions are both important and frequently misunderstood....

It's always struck me as a little bit odd that Active Server Pages, a web server, encourages developers to use VBScript and JScript to write server-side scripts. I mean, the whole point of a web server is that it produces complex strings as blindingly fast as possible, on demand. "Blindingly fast" and "script language" do not really go together......

Every so often some ASP coder out there tries to put a JScript or VBScript object into the Session (or Application) object. Things usually start going horribly wrong shortly thereafter -- either terrible performance ensues or things just break outright. Well, like Groucho says, if it hurts when you do that, don't do that! Understanding why this is a bad idea will take us yet deeper into the land of threading models....

Try this in JScript: window.alert(9.2 * 100.0); You might expect to get 920, but in fact you get 919.9999999999999. What the heck is going on here? ...

It occurs to me that there may be some confusion about what exactly "byref" and "byval" mean in JScript and VBScript. This is frequently a source of confusion, as VBScript has byref behaviour not supported by JScript. ...

While I was waiting for a shuttle the other day (Microsoft has a fleet of shuttle busses that take people all over the campuses) I was thinking about optimization heuristics....

The other day I mentioned my worst customer-impacting mistake ever -- marking a heavily used object with the wrong threading model. A number of people commented to me that it was unusual to see a developer own up to such a mistake in a public forum. (Surprisingly, no one pointed out that it was also odd to do so while talking like a pirate.)...