A VB, VBScript, JavaScript string library based on XPath Functions

At first glance, the string functions of XPath (starts-with, contains, substring-before, substring-after, substring, string-length, normalize-space) might not seem to be that different from those of VB or JavaScript. They are, however, a step up on the abstraction ladder.

For example, substring-after(strURL,'://')means give "me everything after of ://"

In VB you would use
Mid$(strURL, InStr(strURL, "://") + Len("://"))
which means "take the index of the start of ://, add the length of :// and use that value with a Mid$ to get everything after it."

The advantage with the previous example is clear. Let's take an example that's less so.
<xsl:if test="contains(URL,'://')">
means "does the text in URL contain ://?"

In VB, we would write
If Instr(strURL,'://') > 0 Then
Is there any advantage to the XPath here, No? OK, what about JavaScript? Simple, you say, it is as follows
if (strURL.indexOf('://') > 0)

Right? No, wrong. JavaScript strings are zero-based, so the correct code is

I find myself jumping back and forth from VB to JavaScript quite a bit. It is irksome that, when I am want to know if a string "contains" a given substring, I have to remember whether the string is zero or one-based.

In order to take advantage of the higher level functions in XPath in all my programming, I have created, with Fred Baptiste, XPath based modules for VB, VBScript and JavaScript.

Part of the difficulty in creating general reuseable functions is figuring out what to do with boundary conditions. For example, should StartsWith return true if you pass in a zero width match string? Well, you could debate this for a long, long time. If I were a sophomore in college--a time when my parents subsidized such debates--I would happily join in. But now, since I have a job,....

So, does the string "VBXML" begin with a zero length string? The XPath Spec says yes. The XPath expression: starts-with('VBXML','') returns true. Huh? Doesn't make sense to me. But if I followed my preference and then distributed this code to people who know XPath, I would received a lot of "bug" reports. So I have just tried to mimic XPath, using Kay for my reference.

Notes: you can't include a hyphen in VB function names, so following VB protocol, I changed starts-with to StartsWith etc.

Also, XPath is case-sensitive. That is a definitely a big step backward for the VB programmer, so I added a TextCompare enumeration as the last argument to each function, defaulting it to case-sensitive.

Download String Library and VB Program

VBScript!

The VBScript is basically the same as the VB, but with all type declarations taken out.

Download String Library and ASP Tester in VBScript
Thanks to Fred Baptiste (also of Northwoods Software Development)

JavaScript!

For JavaScript, Fred implemented the library by attaching the functions to the String.Prototype.

Download String Library in JavaScript

Following JavaScript's protocol, these methods start with a lower case letter. So, instead of StartsWith, we have startsWith.

BTW, you might be tempted to think that the JavaScript code strTemp.normalize(); changes the variable strTemp. It doesn't. JavaScript strings are immutable. strTemp.normalize() returns a new string.

The JavaScript module like the others, has a boolean flag as the last argument. Without specifying it, the functions are case-sensitive.

Fred also added a trim() function for JavaScript

Download the three modules together

Cheers, Mark mark@lightcc.com

    
	
Notes
	
After is like substring-after 
AfterRev is the same as substring-after, 
	but searches backwards analogous to InstrRev 
Before is like substring-before
BeforeRev see AfterRev   
Contains - this just replaces instr()>0 Why do it? 
	It makes programs more understandable   
EndsWith is not a part of XPath, but it is useful 
Normalize -  (normalize-space) 
	can be done much more quickly with a regex, 
	but the code was already done 	
  Translate - thanks to Fred Baptiste for fixing this