为输入框添加字数提示

计算字符串长度，中文1，其他0.5：

1 var getByteLen=function(str) {
2     if (str == null) return 0;
3     if (typeof str != "string") {
4         str += "";
5     }
6     var count_hanzi = str.replace(/[^x00-xff]/g, "01").length - str.length;
7     var count_feihanzi = str.length - count_hanzi;
8     return parseInt(count_feihanzi / 2) + count_hanzi;
9 }

设置字数提示：

 1     $.fn.TextBoxInputLengthPrompt = function (maxLength) {
 2         var obj = $(this);
 3         var width_obj = parseInt(obj.width());
 4         var height_obj = parseInt(obj.height());
 5         var top_obj = parseInt(obj.offset().top);
 6         var left_obj = parseInt(obj.offset().left);
 7         var length_curr =getByteLen(obj.val());
 8         var length_maxLength = maxLength;
 9         var div = $('<div></div>');
10         obj.parent().append(div);
11         div.css({
12             'width': '180px',
13             'height': '20px'
14         });
15         div.text('字数：' + length_curr + '/' + length_maxLength);
16         obj.keyup(function () {
17             length_curr = getByteLen(obj.val());
18             div.text('字数：' + length_curr + '/' + length_maxLength);
19         })
20         return obj;
21     }

调用：

1 $(selector).TextBoxInputLengthPrompt(count);