var date = Date.parse('Sun May 11,2014');
function format(date) {
date = new Date(date);
var day = ('0' + date.getDate()).slice(-2);
var month = ('0' + (date.getMonth() + 1)).slice(-2);
var year = date.getFullYear();
return year + '-' + month + '-' + day;
}
console.log(format(date));