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?...

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. ...

A reader points out that FormatNumber uses yet a different rounding algorithm. FormatNumber rounds numbers ending in .5's away from zero, not towards evens. He also asks whether FormatNumber, FormatCurrency, etc, actually call into the VBA Format$ code. ...

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?...

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....

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....

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....

My office nameplate was entirely apropos; LoadPicture continued to plague me throughout my career. During the Windows Security Push last year we finally turned it off. When VBScript is running in IE, the LoadPicture method causes an illegal function call exception. Why's that? There's a big security hole in LoadPicture. Not because its buggy, but because it works too well!...

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...

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.)...

I was discussing the difference between executing in local and global scopes the other day. A reader points out something that I forgot to mention – there are two sneaky ways to manipulate the global namespace from an “eval” in Jscript. ...

A reader asked "Why are there two types of multidimentional arrays? What is the difference between the (x)(y) and (x,y) notation?" Good question. There are two kinds of multidimensional arrays, called "rectangular" and "ragged". ...

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?...

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

JScript has an extremely powerful feature: eval takes a string at runtime and treats that string as though it were part of the compile-time text of the program. I added that feature to VBScript version 5, but I did it with three methods: Execute, ExecuteGlobal and Eval. Why three, when JScript makes do with one?...

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!

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I vaguely recall that Waldemar had built a reference implementation of ECMAScript 4 in his metalanguage, and an implementation of the metalanguage in Common Lisp. Like I said, that guy is hard core....

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....

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......

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.

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

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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?...

Yesterday I asked "are JScript strings passed by reference (like JScript objects) or by value (like JScript numbers)?"...

One of the Fundamental Rules of OLE Automation is that for any object, any two calls to GetIdsOfNames with the same string must return the same number. This is so that callers can fetch the dispid once and reuse it, rather than having to fetch it anew every time they try to invoke the dispatch object. But VBScript and JScript do not cache the dispid. Why not? ...

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". ...