Question

I have found the below Javascript recently, and (believe) I understand its operation, but cannot figure out (what appears) to be a ¿regex string class? (“/\W/.test”)

   function AlphaNumericStringCheck(text) 
   {
       if (/\W/.test(text.replace(/^\s+|\s+$/g,""))) return false;
       return true;
   }

Can someone put a name to this technique, so I can research it more?

Answer 1

The /\W/ in your source code is a regular expression literal (MDC link, as MDC is about 18X clearer than the specification). Just as with a string literal (“foo”), a regular expression literal is a way of writing regular expressions in the code. The / characters in a regular expression literal are analogous to the quote characters in a string literal. In a string literal, what’s inside the quotes is the content of the string; in a regular expression literal, what’s inside the / characters is the regular expression. (There can also be flags following the ending /.)

So this:

var rex = /\W/;

…creates a regular expression object for the regular expression \W (match one word character). It’s (essentially) equivalent to:

var rex = new RegExp("\\W");

Note that in the long form, I had to escape the backslash in the string, since backslashes are special in string literals. This is one of the reasons we have regular expression literals: Because it gets very confusing, very quickly, when you have to escape all of your backslashes (backslashes being a significant part of many regular expressions).

Regular expressions are objects, which have properties with functions attached to them (effectively, methods, although JavaScript doesn’t technically have methods per se). So /\W/.test(...) calls the test function on the regular expression object defined by the literal /\W/.