jQuery maxlength插件-判断输入域字符长度

剩余字数：

var $tip = $('剩余字数：');

var $charsLeft = $tip.find('em');

$tip.insertAfter($field);

(function ($) {

$.fn.maxlength = function (settings) {
    //如果只有一个参数，就默认为现实结果的容器
    if (typeof settings == 'string') {
        settings = { feedback : settings };
    }
    //配置参数，缺少的用默认替代
    settings = $.extend({}, $.fn.maxlength.defaults, settings);
    //获取输入域的字符/单词个数
    function length(el) {
        var parts = el.value;
        if ( settings.words )
            parts = el.value.length ? parts.split(/s+/) : { length : 0 };
        return parts.length;
    }
    
    return this.each(function () {
        var field = this,
            $field = $(field),
            //这一点但觉很不好，限制死了外围必须有一个form标签
            $form = $(field.form),
            limit = settings.useInput ? $form.find('input[name=maxlength]').val() : $field.attr('maxlength'),
            $charsLeft = $form.find(settings.feedback);
        
        //添加的
        var $tip = $('剩余字数：');
        var $charsLeft = $tip.find('em');
        $tip.insertAfter($field);
        
        function limitCheck(event) {
            var len = length(this),
                exceeded = len >= limit,
                code = event.keyCode;

            if ( !exceeded )
                return;

            switch (code) {
                case 8:  // allow delete
                case 9:
                case 17:
                case 36: // and cursor keys
                case 35:
                case 37: 
                case 38:
                case 39:
                case 40:
                case 46:
                case 65:
                    return;

                default:
                    return settings.words && code != 32 && code != 13 && len == limit;
            }
        }


        var updateCount = function () {
            var len = length(field),
                diff = limit - len;

            $charsLeft.html( diff || "0" );

            // truncation code
            if (settings.hardLimit && diff                 field.value = settings.words ? 
                    // split by white space, capturing it in the result, then glue them back
                    field.value.split(/(s+)/, (limit*2)-1).join('') :
                    field.value.substr(0, limit);

                updateCount();
            }
        };

        $field.keyup(updateCount).change(updateCount);
        if (settings.hardLimit) {
            $field.keydown(limitCheck);
        }

        updateCount();
    });
};
//这里可以加一个separation，用来自定义分隔符，比如用“，”什么的分割
$.fn.maxlength.defaults = {
    useInput : false,
    hardLimit : true,
    feedback : '.charsLeft',
    words : false
};

})(jQuery);