lib/Ext/core/class/Loader.js
function(className) {
            var path = '',
                paths = this.config.paths,
                prefix = this.getPrefix(className);

            if (prefix.length > 0) {
                if (prefix === className) {
                    return paths[prefix];
                }

                path = paths[prefix];
                className = className.substring(prefix.length + 1);
            }

            if (path.length > 0) {
                path += '/';
            }

            return path.replace(/\/\.\//g, '/') + className.replace(/\./g, "/") + '.js';
        }
function(className) {
            var path = '',
                paths = this.config.paths,
                prefix = this.getPrefix(className);

            if (prefix.length > 0) {
                if (prefix === className) {
                    return paths[prefix];
                }

                path = paths[prefix];
                className = className.substring(prefix.length + 1);
            }

            if (path.length > 0) {
                path += '/';
            }

            return path.replace(/\/\.\//g, '/') + className.replace(/\./g, "/") + '.js';
        }
Translates a className to a file path by adding the
the proper prefix and converting the .'s to /'s. For example:

Ext.Loader.setPath('My', '/path/to/My');

alert(Ext.Loader.getPath('My.awesome.Class')); // alerts '/path/to/My/awesome/Class.js'

Note that the deeper namespace levels, if explicitly set, are always resolved first. For example:

Ext.Loader.setPath({
'My': '/path/to/lib',
'My.awesome': '/other/path/for/awesome/stuff',
'My.awesome.more': '/more/awesome/path'
});

alert(Ext.Loader.getPath('My.awesome.Class')); // alerts '/other/path/for/awesome/stuff/Class.js'

alert(Ext.Loader.getPath('My.awesome.more.Class')); // alerts '/more/awesome/path/Class.js'

alert(Ext.Loader.getPath('My.cool.Class')); // alerts '/path/to/lib/cool/Class.js'

alert(Ext.Loader.getPath('Unknown.strange.Stuff')); // alerts 'Unknown/strange/Stuff.js'

@param {String} className
@return {String} path