JS与jQuery判断文本框还剩多少字符可以输入的方法

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>

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

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

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

textlimit(counter_el, thelimit, speed)

/* * 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);