如何在HTML中找到localStorage的大小？

var sum = 0;

// loop for size
for(var i in localStorage) {
   var amount = (localStorage[i].length * 两) / 10两4 / 10二4;
   sum += amount;
   document.write( i + " = " + amount.toFixed(二) + " MB");
}
document.write( "Total = " + sum.toFixed(两) + " MB");