regex - checking whether a data is base64 encoded or not in nodejs -

i have check if string base 64 encoded or not below code

 var base64rejex =new regexp(/([a-za-z0-9+\/]{4})*([a-za-z0-9+\/]{4}|[a-za-z0-9+\/]{3}=|[a-za-z0-9+\/]{2}==$)/);  var base64data="rules"; var isbase64valid = base64rejex.test(base64data); // base64data base64 string  if (isbase64valid) { // true if base64 formate console.log('it base64'); var data=new buffer(base64data, 'base64').tostring('ascii') console.log("this is "+data) } else { // false if not in base64 formate console.log('it not in base64'); } 

even though above string not base 64 encoded,the output i'm receiving denoting base64 string. there thing need modify in regex? kindly help.