How to convert date format dd-mmm-yy to yyyy-mm-dd in javascript

function changeDateFormat(dateToBeFormated){
var months = {'jan': '01', 'feb': '02', 'mar': '03', 'apr': '04', 'may': '05', 'jun': '06', 'jul': '07', 'aug': '08', 'sep': '09', 'oct': '10', 'nov': '11', 'dec': '12'};
var arr = dateToBeFormated.split('-'); // split based on '-'
var year = '20'+ arr[2] ; // add '20' before year
var month = months[arr[1].toLowerCase()] ; // convert month into lower
var day = arr[0] ;
if (day < 10) day = "0" + day; // add '0' if date is less then 10.
return [year,month,day].join('-'); // join value according to format.
}