Answer by kiranvj for Detecting an "invalid date" Date instance in JavaScript

function isValidDate(strDate) {
    var myDateStr= new Date(strDate);
    if( ! isNaN ( myDateStr.getMonth() ) ) {
       return true;
    }
    return false;
}

Call it like this

isValidDate(""2015/5/2""); // => true
isValidDate(""2015/5/2a""); // => false