给textarea增加长度限制的几种方法

来源：互联网发布：python http接口开发编辑：程序博客网时间：2024/06/10 03:25

最简单的：

<textarea name="A" cols="45" rows="2" onKeyDown='if (this.value.length>=20){event.returnValue=false}'>aaaa</textarea>
简单有效，但问题是输入20个字符后边删除键、光标键通通失效，未够20个字符时粘贴一段长文字也可以突破限制。

最粗暴的：

用户会很疑惑，我明明录入了内容怎么一放手都没了, 而且光标键都跳到后面。

最牛的：

<html>
<head>
<title>IE和FireFox中的textarea长度限制</title>
</head>
<body>
<textarea maxlength="10" onpropertychange="onmyinput(this)" oninput="return onmyinput(this)" onPaste="return onmypaste(this);" onKeyPress="return onmykeypress(this);"></textarea>
//功能：IE和FireFox中的textarea长度限制
//作者：铁血骷髅
<script type="text/javascript">
function onmyinput(o)
{
if(o.value.length>=o.getAttribute("maxlength"))
{
if(o.value.length>o.getAttribute("maxlength"))
o.value = o.value.substring(0,o.getAttribute("maxlength"));
return false;
}
return true;
}
function mygetclipdata()
{
if(!document.all)
{
netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
var clip = Components.classes['@mozilla.org/widget/clipboard;1'].createInstance(Components.interfaces.nsIClipboard);
var trans = Components.classes['@mozilla.org/widget/transferable;1'].createInstance(Components.interfaces.nsITransferable);
trans.addDataFlavor('text/unicode');
var str = Components.classes["@mozilla.org/supports-string;1"].createInstance(Components.interfaces.nsISupportsString);
clip.getData(trans,clip.kGlobalClipboard);
var str=new Object();
var strLength=new Object();
trans.getTransferData("text/unicode",str,strLength);
if (str)
str=str.value.QueryInterface(Components.interfaces.nsISupportsString);
var pastetext;
if (str)
pastetext=str.data.substring(0,strLength.value / 2);
return pastetext;
}
else
{
return window.clipboardData.getData("Text");
}
}
function mysetclipdata(o)
{
if(!document.all)
{
netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
var clip = Components.classes['@mozilla.org/widget/clipboard;1'].createInstance(Components.interfaces.nsIClipboard);
var trans = Components.classes['@mozilla.org/widget/transferable;1'].createInstance(Components.interfaces.nsITransferable);
trans.addDataFlavor("text/unicode");
var str = Components.classes["@mozilla.org/supports-string;1"].createInstance(Components.interfaces.nsISupportsString);
str.data=o;
trans.setTransferData("text/unicode",str,o.length*2);
var clipid=Components.interfaces.nsIClipboard;
clip.setData(trans,null,clipid.kGlobalClipboard);
}
else
{
window.clipboardData.setData("Text",o);
}
}
function onmypaste(o)
{
var nMaxLen=o.getAttribute? parseInt(o.getAttribute("maxlength")):"";
if(!document.all)
{
alert("不可能执行的代码");
}
else
{

if(document.selection.createRange().text.length>0)
{
   var ovalueandclipboarddata = o.value +window.clipboardData.getData("Text");
   if(o.getAttribute && ovalueandclipboarddata.length-document.selection.createRange().text.length>nMaxLen)
   {
    if(window.clipboardData.getData("Text").substring(0,document.selection.createRange().text.length+nMaxLen-o.value.length)!="")
     window.clipboardData.setData("Text",window.clipboardData.getData("Text").substring(0,document.selection.createRange().text.length+nMaxLen-o.value.length));
    else
     return false;
   }
}
else
{
   var ovalueandclipboarddata = o.value +window.clipboardData.getData("Text");
   if(o.getAttribute && ovalueandclipboarddata.length>nMaxLen)
   {
    if(ovalueandclipboarddata.substring(0,nMaxLen-o.value.length)!="")
     window.clipboardData.setData("Text",ovalueandclipboarddata.substring(0,nMaxLen-o.value.length));
    else
     return false;
   }
}
return true;
}
}
function onmykeypress(o)
{
if(!document.all)
{
var nMaxLen=o.getAttribute? parseInt(o.getAttribute("maxlength")):"";

if(onmykeypress.caller.arguments[0].ctrlKey == true)
{
if(onmykeypress.caller.arguments[0].which==118)
{

    if(o.selectionStart<o.selectionEnd)
    {
     var ovalueandclipboarddata = o.value + mygetclipdata();
     if(o.getAttribute && (ovalueandclipboarddata.length-o.selectionEnd + o.selectionStart>nMaxLen))
     {
      if(mygetclipdata().substring(0,o.selectionEnd - o.selectionStart+nMaxLen-o.value.length)!="")
       mysetclipdata(mygetclipdata().substring(0,o.selectionEnd - o.selectionStart+nMaxLen-o.value.length));
      else
       return false;
     }
    }
    else
    {
     var ovalueandclipboarddata = o.value +mygetclipdata();
     if(o.getAttribute && ovalueandclipboarddata.length>nMaxLen)
     {
      if(ovalueandclipboarddata.substring(0,nMaxLen-o.value.length)!="")
       mysetclipdata(ovalueandclipboarddata.substring(0,nMaxLen-o.value.length));
      else
       return false;
     }
    }
    return true;

}
}

if(onmykeypress.caller.arguments[0].which==0 || onmykeypress.caller.arguments[0].which==8)
   return true;
if(o.value.length>=o.getAttribute("maxlength"))
{
   if(o.selectionStart<o.selectionEnd)
    return true;
   if(o.value.length>o.getAttribute("maxlength"))
    o.value = o.value.substring(0,o.getAttribute("maxlength"));
   return false;
}
else
   return true;

}
else
{
if(document.selection.createRange().text.length>0)
   return true;
if(o.value.length>=o.getAttribute("maxlength"))
   return false;
else
   return true;
}
}
</script>
</body>
</html>

只有想不到，没有做不到，写这代码的哥们太太太牛了。