How to convert American date format to European

Question

from : 5/19/2011

to : 2011-05-19

I need it to raise an error when it finds that it cannot be real like 5/40/2011 etc.

Answer 1

Keep it simple:

[edit] right, you wanted a check too, so added fn chkDat:

function zeroPad(n){
  return (parseInt(n,10)<10 ? '0' : '') + n;
}

var usdat = '5/19/2011'.split('/')
    ,eudat = [usdat[2],zeroPad(usdat[0]),zeroPad(usdat[1])];

alert(chkDat(usdat,eudat); //=> true
alert(eudat.join('-'));    //=> '2011-05-19'

function chkDat(orig,eu){
   var eu = new Date(eu.join('/'));
   return   eu.getMonth()+1 === parseInt(orig[0],10)
         && eu.getDate() === parseInt(orig[1],10)
         && eu.getFullYear() === parseInt(orig[2],10)
   ;
}

Note the date format you're after is called Calendar date (ISO 8601).