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计算文本域剩佘长度的js代码

JS 计算文本域剩余字数 
<textarea cols="20" rows="4" onkeyup="displaySpareNumber(this,10)" onchange="displaySpareNumber(this,10)"></textarea> 
<img src="/_New/_cj/myeditor/sysimage/space.gif" class="ewebeditor__script" _ewebeditor_fake_tag="script" _ewebeditor_fake_value="%3Cscript%20type%3D%22text%2Fjavascript%22%20language%3D%22JavaScript%22%3E%20%0D%0Afunction%20displaySpareNumber(_this%2Csize)%20%0D%0A%7B%20%0D%0Avar%20spareNumber%3Ddocument.getElementById(%22spareNumber%22)%3B%20%0D%0A%2F%2F%E6%B1%89%E5%AD%97%E9%95%BF%E5%BA%A6%20%0D%0Avar%20len%3D_this.value.replace(%2F%5B%5E%5Cx00-%5Cxff%5D%2Fgi%2C'xx').length%3B%20%0D%0Avar%20snum%3DparseInt(size)-len%3B%20%0D%0AspareNumber.value%3Dsnum%3B%20%0D%0Aif(snum%3C0)%20%0D%0A%7B%20%0D%0Aif(_this.value.length!%3Dlen)%20%0D%0A%7B%20%0D%0Aif((len-_this.value.length)%3E(size%2F2))%20%0D%0A%7B%20%0D%0A_this.value%3D_this.value.substring(0%2Csize%2F2)%3B%20%0D%0A%7D%20%0D%0Aelse%20%0D%0A%7B%20%0D%0A_this.value%3D_this.value.substring(0%2Csize-(len-_this.value.length))%3B%20%0D%0A%7D%20%0D%0A%7D%20%0D%0Aelse%20%0D%0A%7B%20%0D%0A_this.value%3D_this.value.substring(0%2Csize)%3B%20%0D%0A%7D%20%0D%0AspareNumber.value%3D0%3B%20%0D%0Areturn%3B%20%0D%0A%7D%20%0D%0A%7D%20%0D%0A%3C%2Fscript%3E"> 
剩 <input id="spareNumber" name="spareNumber" value="10" size="1"/> 
<br><br> 
注： <br> 
displaySpareNumber(this,10) <br> 
与 <br> 
<input id="spareNumber" name="spareNumber" value="10" size="1"/> <br> 
中的10是你定义的内容长度.

　　 [Ctrl+A 全选注:如需引入外部Js需刷新才能执行]

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