限制字数（半角全角）

<script type="text/javascript"> 
function checkLength() { 
var which = $("#content").val();
var totalLength = 0;
var maxChars = 140; 
var list = which.split("");
//if (list.length > maxChars) 
//list.value = list.value.substring(0,maxChars); 
for(var i = 0; i < list.length; i++) {
var s = list[i];
   if (s.match(/[\u0000-\u00ff]/g)) { //半角
    totalLength += 0.5;
   } else if (s.match(/[\u4e00-\u9fa5]/g)) { //中文 
    totalLength += 1;
   } else if (s.match(/[\uff00-\uffff]/g)) { //全角
    totalLength +=1;
   }
  }  
var curr = maxChars - totalLength; 
if(curr >= 0){
    $("#shuru").show();
    $("#chaochu").hide();
    $("#content_chaochu").val(1);//在限制范围内为1
    document.getElementById("chLeft").innerHTML = parseInt(curr.toString()); 
}else{
    var chao = totalLength - maxChars;
    if(chao > 0){
        $("#chLeft_chao").css('color','#FF0000');
        $("#shuru").hide();
        $("#chaochu").show();
        $("#content_chaochu").val(2);//超出范围内为2
        document.getElementById("chLeft_chao").innerHTML = parseInt(chao.toString());
    } 
}
return false;
} 
</script>

<p class="clearfix">
            <span class="fr" id="shuru">还可以输入<span class="w-fs" id="chLeft">140</span>字</span><span class="weibo-tit"></span>
            <span class="fr" id="chaochu" style="display:none">已经超出<span class="w-fs" id="chLeft_chao">140</span>字</span><span class="weibo-tit"></span></p>

<textarea name="content" id="content" class="weibo-area" onkeyup="checkLength()"></textarea>
<input type="hidden" id="content_chaochu" value="1" />