I am currently trying to add my own extension to showdown using the ghost blogging platform. I am trying to make it so someone can type map and then a uk postcode and have it rendered to a map, like so [map bh278bf]. I have made sure the maps.js extension has been added and works as I have tested it. However my Regex knowledge is practically non-existent. I have got the RegEx to work here in Regexr.com, but when I run it nothing happens, I have used the same codepen and it also doesn't work and I have no idea what to do. I need some assistance in identifying the string! 
The Expression:
/(\[map )([A-PR-UWYZ0-9][A-HK-Y0-9][AEHMNPRTVXY0-9]?[ABEHMNPRVWXY0-9]?[0-9][ABD-HJLN-UW-Z]{2}|GIR 0AA)(\])/igm
The extension (maps.js)
(function(){
    var maps = function(converter) {
        return [
            { 
                type: 'output', 
                filter: function(source) {
                    return source.replace(/(\[map )([A-PR-UWYZ0-9][A-HK-Y0-9][AEHMNPRTVXY0-9]?[ABEHMNPRVWXY0-9]?[0-9][ABD-HJLN-UW-Z]{2}|GIR 0AA)(\])$/gim, function(match) {
                        return "<span>Map will go here</span>";
                    });
                }
            }
        ];
    };
    // Client-side export
    if (typeof window !== 'undefined' && window.Showdown && window.Showdown.extensions) { window.Showdown.extensions.prettify = maps; }
    // Server-side export
    if (typeof module !== 'undefined') module.exports = maps;
}());
 
     
    