判断文本框还剩多少字符可以输入

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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 * vsync.design@gmail.com*/(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);

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