Format JavaScript date as yyyy-mm-dd

#short
#javascript
#date
#formatting
#datetime-format
#date-format
I have a date with the format Sun May 11,2014. How can I convert it to 2014-05-11 using JavaScript?

function taskDate(dateMilli) {
var d = (new Date(dateMilli) + '').split(' ');
d[2] = d[2] + ',';

return [d[0], d[1], d[2], d[3]].join(' ');
}


The code above gives me the same date format, sun may 11,2014. How can I fix this?