JS在光标处插入

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>无标题文档</title>
</head>
<body>
<form id="form1" name="form1" method="post" action="">
<label>
   <textarea name="test1" id="test1" cols="45" rows="5">这是默认内容，嘿嘿，测试一下!</textarea>
   <br />
   <br />
   <input name="tag" type="text" id="tag" value="AAA" />
    <br />
   <br />
   <a href="javascript:void(0);" onclick="insertAtCursor($('test1'), $('tag').value);">插入</a>
</label>
</form>
</body>
</html>

<script type="text/javascript">

   function $(id) { return document.getElementById(id); }

   // 在光标处插入字符串
   // myField   文本框对象
   // 要插入的值
    function insertAtCursor(myField, myValue)
   {
        //IE support
        if (document.selection)
       {
            myField.focus();
            sel           = document.selection.createRange();
            sel.text   = myValue;
            sel.select();
        }
        //MOZILLA/NETSCAPE support
        else if (myField.selectionStart || myField.selectionStart == '0')
       {
            var startPos   = myField.selectionStart;
            var endPos       = myField.selectionEnd;
            // save scrollTop before insert
            var restoreTop   = myField.scrollTop;
            myField.value   = myField.value.substring(0, startPos) + myValue + myField.value.substring(endPos, myField.value.length);
            if (restoreTop > 0)
           {
                // restore previous scrollTop
                myField.scrollTop = restoreTop;
            }
            myField.focus();
            myField.selectionStart   = startPos + myValue.length;
            myField.selectionEnd   = startPos + myValue.length;
        } else {
            myField.value += myValue;
            myField.focus();
        }
    }

</script>