DevDating.js

(function() {
    
    var rows = map[0].length;
    var cols = map.length;
    
    String.prototype.replaceAt=function(index, character) 
    {
        return this.substr(0, index) + character + this.substr(index+character.length);
    }
     
    var dropRocks = function(c)
    { 
        for(var r = rows-1; r >= 0; r--)
        {
            if(map[c][r] == 'o' && map[c][r+1] == '.')
            { 
                map[c] = map[c].replaceAt(r, '.');
                map[c] = map[c].replaceAt(r+1, 'o');
                r = rows-1; 
            }
        } 
    }
    
    var i = 0;
    for(i = 0; i < cols; i++)
    {
        dropRocks(i);
    }
    
    console.dir(map);
    return map;
    
})();