[Javascript] Wildcard string matching / globbing

Most Javascript programmers are more than happy with regular expressions. However, there are times when something like wildcards ('?' for one character and '*' for many) would be helpful.

Jack Handy's first and last (it seems) article on CodeProject implemented a wildcard string compare (also known as 'globbing') function in C. Below I present my port of that function to Javascript.

As a newbie Javascript programmer (4 weeks in as of 2010-11-30), I've pleasantly surprised by the expressive power of Javascript. What has caught my eye recently is the power of .prototype., so this implementation of matchesWild() is declared as a prototype extending the String class.

Here's the code, with some commentary:

String.prototype.matchesWild = function( wildCard ) {
        // Written by Jack Handy - jakkhandy@hotmail.com
        //  http://www.codeproject.com/KB/string/wildcmp.aspx
        // Made to work in javascript by Bruce M. Axtens - bruce@strapper.net

Apart from the comments, notice the way Javascript adds a method to an object, defining an anonymous function with, in this case, one parameter, and assigning it as a prototype.

        var nCp = 0;
        var nMp = 0;
        var nWild = 0;
        var nThis = 0;

The C version did all kinds of interesting things with pointers. Javascript doesn't have that kind of stuff (AFAICT), so I had to do the equivalent with numeric offsets and substr().

Perhaps there are better ways of doing this. I have tried to do this kind of thing before, but this code seems to do a pretty good job of it and hasn't failed thus far.

What should be noted, and perhaps dealt with, is that there is no explicit check for calling the method without a parameter. If one does this, an error is raised. Chrome's V8 raises "TypeError: Cannot call method 'substr' of undefined".

        while ( ( this.substr( nThis, 1 ) ) && ( wildCard.substr( nWild, 1 ) !== '*')) {
                if ( ( wildCard.substr( nWild, 1 ) !== this.substr( nThis, 1 ) ) && 
                        ( wildCard.substr( nWild, 1 ) !== '?') ) 
                                return false;
                nWild++;
                nThis++;
        }

        while ( this.substr( nThis, 1 ) ) {
                if ( wildCard.substr( nWild, 1 ) === '*' ) {
                        if ( !wildCard.substr( ++nWild, 1 ) ) 
                                return true;
                        nMp = nWild;
                        nCp = nThis+1;
                } else if ( ( wildCard.substr( nWild, 1 ) === this.substr( nThis, 1 ) ) || 
                        ( wildCard.substr( nWild, 1 ) === '?' ) ) {
                                nWild++;
                                nThis++;
                } else {
                        nWild = nMp;
                        nThis = nCp++;
                }
        }

        while ( wildCard.substr( nWild, 1 ) === '*' ) 
                nWild++;
        return !wildCard.substr( nWild, 1 );
}

And now some examples (evaluated using macports's JavaScript-C 1.7.0 2007-10-03)

        var i;
        var a = ['kangaroo', 'koala', 'goanna', 'quoll', 'bunyip', 'yowie', 'bandicoot', 'numbat'];

        print('select everything with an \'o\' at the second character position');
        for ( i = 0; i < a.length; i++ ) {
                if ( a[ i ].matchesWild( '?o*' ) )  print( 'item(' + i + ')=' + a[i] );
        }
        print("--------------------");
        print('select everything ending with \'a\'');
        for ( i = 0; i < a.length; i++ ) {
                if ( a[ i ].matchesWild( '*a' ) )  print( 'item(' + i + ')=' + a[i] );
        }
        print("--------------------");
        print('select everything with at least two \'a\' characters');
        for ( i = 0; i < a.length; i++ ) {
                if ( a[ i ].matchesWild( '*a*a*' ) )  print( 'item(' + i + ')=' + a[i] );
        }
        print("--------------------");
        print('select everything with an \'oo\'' );
        for ( i = 0; i < a.length; i++ ) {
                if ( a[ i ].matchesWild( '*oo*' ) )  print( 'item(' + i + ')=' + a[i] );
        }
        print("--------------------");
        print('select everything with at least one \'z\' character');
        for ( i = 0; i < a.length; i++ ) {
                if ( a[ i ].matchesWild( '*z*' ) )  print( 'item(' + i + ')=' + a[i] );
        }
        print("--------------------");

Outputs:

select everything with an 'o' at the second character position
item(1)=koala
item(2)=goanna
item(5)=yowie
--------------------
select everything ending with 'a'
item(1)=koala
item(2)=goanna
--------------------
select everything with at least two 'a' characters
item(0)=kangaroo
item(1)=koala
item(2)=goanna
--------------------
select everything with an 'oo'
item(0)=kangaroo
item(6)=bandicoot
--------------------
select everything with at least one 'z' character
--------------------

More Javascript coming soon. In the meantime, enjoy.

© Bruce M. Axtens, 2010