如何在HTML中找到localStorage的大小？

var sum = 0;// loop for sizefor(var i in localStorage) {   var amount = (localStorage[i].length * 2) / 1024 / 1024;   sum += amount;   document.write( i + " = " + amount.toFixed(2) + " MB");}document.write( "Total = " + sum.toFixed(2) + " MB");