如何防止在达到一定字符数后向文本区域输入内容？

使用下面的代码，任何超过指定最大值的输入都将被删除。但这会产生一种效果，即键入字符后立即将其删除。我宁愿简单地阻止输入字符。

<textarea  id="textarea" onKeyDown="limitText()" onKeyUp="limitText()">
</textarea> 
<span name="charcount_text" id="charcount_text"></span>

  <script type="text/javascript">
    function limitText() {
      var count = document.getElementById('textarea').value.length;
      var remaining = 4000 - count;
      if(remaining <= 0) {
        document.getElementById('charcount_text').innerHTML = '4000 character limit reached.' ;
        document.getElementById('textarea').value = document.getElementById('textarea').value.substring(0, 4000);
      } else if(remaining <= 50) {
        document.getElementById('charcount_text').innerHTML = '4000 character limit, ' + remaining  + ' remaining.';
      } else {
        document.getElementById('charcount_text').innerHTML = '';
      }
    }
  </script>

Use the maxlength属性：

<textarea  id="textarea" maxlength="4000" onkeyup="limitText()"></textarea>

function limitText() {
  var ta= document.getElementById('textarea'),
      count= ta.value.length,
      ml= ta.maxLength,
      remaining= ml - count,
      cc= document.getElementById('charcount_text');

  if(remaining <= 0) {
    cc.innerHTML = ml+' character limit reached.' ;
  } else if(remaining <= 50) {
    cc.innerHTML = ml+' character limit, ' + remaining  + ' remaining.';
  } else {
    cc.innerHTML = '';
  }
}

Fiddle http://jsfiddle.net/yhocak08/