You can use the io module: http://yuilibrary.com/yui/docs/io/
Example:
YUI().use('io', function (Y) {
Y.io('/root/www/appConfig.json', {
on: {
start: function () {
Y.log('start');
},
success: function (id, o) {
var json = Y.JSON.parse(o.responseText);
Y.log(json);
},
failure: function () {
Y.log('failure');
}
},
context: this
});
});