Jquery插件--判断文本框还剩多少字符可以输入

javascript

function $(id) {  

    return document.getElementById(id);  

}  

  

var maxLen=255;  

function checkMaxInput(){  

    if($("summary").value.length>maxLen){  

        $("summary").value=$("summary").value.substring(0,maxLen);  

    }else{  

        $("leaves").innerHTML=maxLen-$("summary").value.length;  

    }  

}  

  
    

   
     
<tr>  

  <td>摘要：</td>  

  <td>  

    <html:textarea  property="summary"  rows="5" cols="60"  onkeyup="checkMaxInput()"/>  

    <br>  

     还可以输入<span class="red" id="leaves">255</span>个字符  

   </td>  

</tr>  




  
    

jQuery插件textlimit实现Javascript统计和限制字符个数功能 

http://www.biuuu.com/p870.html 

使用jQuery插件textlimit可以实现统计和限制字符个数功能，可应用于文本框与文本区域， 
当输入文字时textlimit插件会及时统计当前文本框与文本区域中的字符个数，如果达到限制数则不允许输入，同时可设置字符删除速度， 

使用实例 
一，包含文件部分 

   1. <script type="text/javascript" src="jquery.js"></script> 
   2. <script type="text/javascript" src="textlimit.js"></script> 

二，HTML部分 

   1. <input type="text" name="test" value="" id="test" /><span>20</span>/256 

三，Javascript部分 

   1. <script type="text/javascript"> 
   2. jQuery(document).ready(function(){ 
   3. jQuery("#test").textlimit("span",256); 
   4. }); 
   5. </script> 

当在ID为test的文本框中输入文字时，textlimit插件统计当前输入字符个数并显示在一个span的元素中，如上效果图，textlimit接口如下： 

   1. textlimit(counter_el, thelimit, speed) 

接口参数说明： 
counter_el表示显示当前统计个数的选择器标签，如：span 
thelimit表示限制个数，也就是最多可输入的个数，如：256 
speed表示删除字符速度，默认为15，注意，如果不需要可设置为-1，但不能是0 

注意：英文字符与汉字字符都统计为一个字符 

textlimit插件统计和限制字符数非常简单，具体大家可以看看textlimit的库文件，非常值得推荐。 

  
    

   
     
/* 

 * TextLimit - jQuery plugin for counting and limiting characters for input and textarea fields 

 *  

 * pass '-1' as speed if you don't want the char-deletion effect. (don't just put 0) 

 * Example: jQuery("Textarea").textlimit('span.counter',256) 

 * 

 * $Version: 2009.07.25 +r2 

 * Copyright (c) 2009 Yair Even-Or 

 * [email protected] 

*/  

(function(jQuery) {  

    jQuery.fn.textlimit=function(counter_el, thelimit, speed) {  

        var charDelSpeed = speed || 15;  

        var toggleCharDel = speed != -1;  

        var toggleTrim = true;  

        var that = this[0];  

        var isCtrl = false;   

        updateCounter();  

          

        function updateCounter(){  

            if(typeof that == "object")  

                jQuery(counter_el).text(thelimit - that.value.length+" characters remaining");  

        };  

          

        this.keydown (function(e){   

            if(e.which == 17) isCtrl = true;  

            var ctrl_a = (e.which == 65 && isCtrl == true) ? true : false; // detect and allow CTRL + A selects all.  

            var ctrl_v = (e.which == 86 && isCtrl == true) ? true : false; // detect and allow CTRL + V paste.  

            // 8 is 'backspace' and 46 is 'delete'  

            if( this.value.length >= thelimit && e.which != '8' && e.which != '46' && ctrl_a == false && ctrl_v == false)  

                e.preventDefault();  

        })  

        .keyup (function(e){  

            updateCounter();  

            if(e.which == 17)  

                isCtrl=false;  

  

            if( this.value.length >= thelimit && toggleTrim ){  

                if(toggleCharDel){  

                    // first, trim the text a bit so the char trimming won't take forever  

                    // Also check if there are more than 10 extra chars, then trim. just in case.  

                    if ( (this.value.length - thelimit) > 10 )  

                        that.value = that.value.substr(0,thelimit+100);  

                    var init = setInterval  

                        (   

                            function(){   

                                if( that.value.length <= thelimit ){  

                                    init = clearInterval(init); updateCounter()   

                                }  

                                else{  

                                    // deleting extra chars (one by one)  

                                    that.value = that.value.substring(0,that.value.length-1); jQuery(counter_el).text('Trimming... '+(thelimit - that.value.length));  

                                }  

                            } ,charDelSpeed   

                        );  

                }  

                else this.value = that.value.substr(0,thelimit);  

            }  

        });  

          

    };  

})(jQuery);