为输入框添加字数提示

  计算字符串长度，中文1，其他0.5：

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

  设置字数提示：

    $.fn.TextBoxInputLengthPrompt = function (maxLength) {
        var obj = $(this);
        var width_obj = parseInt(obj.width());
        var height_obj = parseInt(obj.height());
        var top_obj = parseInt(obj.offset().top);
        var left_obj = parseInt(obj.offset().left);
        var length_curr =getByteLen(obj.val());
        var length_maxLength = maxLength;
        var div = $('<div></div>');
        obj.parent().append(div);
        div.css({
            'width': '180px',
            'height': '20px'
        });
        div.text('字数：' + length_curr + '/' + length_maxLength);
        obj.keyup(function () {
            length_curr = getByteLen(obj.val());
            div.text('字数：' + length_curr + '/' + length_maxLength);
        })
        return obj;
    }

  调用：

$(selector).TextBoxInputLengthPrompt(count);