js 计算 字符串 字节数

function (str) {
        var length = 0;
        if (!!str && "string" == typeof str) {
            for (var i = 0; i < str.length; i++) {
                if (str.charCodeAt(i) > 255) {
                    length += 2;
                } else {
                    length++;
                }
            }

        }
        return length;
   }