Calculates localStorage key and total size occupied by data in MB

local_storage_size.js

var total = 0;
for (var key in localStorage) {
  var keySize = ((localStorage[key].length * 2) / 1024 / 1024).toFixed(2);
  console.log(key + '=' + keySize + ' MB');
  total += parseFloat(keySize);
}
console.log('total=' + total.toFixed(2) + ' MB');

'Functional version'