weird output of crypto module in node

weirdcrypto.js

var fs=require('fs'), c=require('crypto'), assert=require('assert');

var h = c.createHash('SHA256');
h.update('12345');
h.update('54321');
var key=h.digest('base64');
var enc = c.createCipher('AES-128-CBC', key);
var a=enc.update('12345678901234567890', 'utf8', 'base64');
var cipherText = enc.final('base64');

var dec = c.createDecipher('AES-128-CBC', key);
a = dec.update(cipherText, 'base64', 'utf8');
a = dec.final(cipherText, 'utf8');
console.log(a);