function getDateString(str) {
let months = ['ENE', 'FEB', 'MAR', 'ABR', 'MAY', 'JUN', 'JUL', 'AGO', 'SEP', 'OCT', 'NOV', 'DIC'];
if(!str) return;
if(str.length !== 11) return;
str = str.toUpperCase();
if(!months.includes(str.substring(3, 6))) return;
let dateStr = str.substring(0,3) + (months.indexOf(str.substring(3, 6)) + 1).toString().padStart(2, '0') + str.substring(6);
return dateStr;
}
let fechas = [
'12-Ene-2021',
'04-feb-2020',
'15-JUN-1976'
]
fechas.forEach(f => {
console.log( getDateString(f));