本文實例講述了JS與jQuery判斷文本框還剩多少字符可以輸入的方法。分享給大家供大家參考，具體如下：

javascript部分：

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;  }}

HTML部分：

<tr> <td>摘要：</td> <td>  <html:textarea property="summary" rows="5" cols="60" onkeyup="checkMaxInput()"/>  <br>   還可以輸入<span class="red" id="leaves">255</span>個字符  </td></tr>

jQuery插件textlimit實現(xiàn)Javascript統(tǒng)計和限制字符個數(shù)功能

使用jQuery插件textlimit可以實現(xiàn)統(tǒng)計和限制字符個數(shù)功能，可應用于文本框與文本區(qū)域，當輸入文字時textlimit插件會及時統(tǒng)計當前文本框與文本區(qū)域中的字符個數(shù)，如果達到限制數(shù)則不允許輸入，同時可設置字符刪除速度，

使用實例

一、包含文件部分

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

二、HTML部分

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

三、Javascript部分

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

當在ID為test的文本框中輸入文字時，textlimit插件統(tǒng)計當前輸入字符個數(shù)并顯示在一個span的元素中，如上效果圖，textlimit接口如下：

textlimit(counter_el, thelimit, speed)

接口參數(shù)說明：

注意：英文字符與漢字字符都統(tǒng)計為一個字符

textlimit插件統(tǒng)計和限制字符數(shù)非常簡單，具體大家可以看看textlimit的庫文件，非常值得推薦。

/* * 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);