<html>
<head>
<title>TEST</title>
<style>
body,td{
    font-family: verdana, arial, helvetica, sans-serif;
    font-size: 12px;
}
</style>
<script type=”text/javascript”>
    var start=0;
    var end=0;
    function add(){       
        var textBox = document.getElementById(“ta”);
        var pre = textBox.value.substr(0, start);
        var post = textBox.value.substr(end);
        textBox.value = pre + document.getElementById(“inputtext”).value + post;
    }
    function savePos(textBox){
        //如果是Firefox(1.5)的话,方法很简单&lt;br />
        if(typeof(textBox.selectionStart) == “number”){
            start = textBox.selectionStart;
            end = textBox.selectionEnd;
        }
        //下面是IE(6.0)的方法,麻烦得很,还要计算上'”n’
        else if(document.selection){
            var range = document.selection.createRange();
            if(range.parentElement().id == textBox.id){
                // create a selection of the whole textarea
                var range_all = document.body.createTextRange();
                range_all.moveToElementText(textBox);
                //两个range,一个是已经选择的text(range),一个是整个textarea(range_all)
                //range_all.compareEndPoints()比较两个端点,如果range_all比range更往左(further to the left),则                //返回小于0的值,则range_all往右移一点,直到两个range的start相同。&lt;br />
                // calculate selection start point by moving beginning of range_all to beginning of range
                for (start=0; range_all.compareEndPoints(“StartToStart”, range) < 0; start++)
                    range_all.moveStart(‘character’, 1);
                // get number of line breaks from textarea start to selection start and add them to start
                // 计算一下"n
                for (var i = 0; i <= start; i ++){
                    if (textBox.value.charAt(i) == ‘n’)
                        start++;
                }
                // create a selection of the whole textarea
                 var range_all = document.body.createTextRange();
                 range_all.moveToElementText(textBox);
                 // calculate selection end point by moving beginning of range_all to end of range
                 for (end = 0; range_all.compareEndPoints(‘StartToEnd’, range) < 0; end ++)
                     range_all.moveStart(‘character’, 1);
                     // get number of line breaks from textarea start to selection end and add them to end
                     for (var i = 0; i <= end; i ++){
                         if (textBox.value.charAt(i) == ‘n’)
                             end ++;
                     }
                }
            }
        document.getElementById(“start”).value = start;
        document.getElementById(“end”).value = end;
    }
</script>
</head>
<body>
<form action=”a.cgi”>
<table border=”1″ cellspacing=”0″ cellpadding=”0″>
    <tr>
        <td>start: <input type=”text” id=”start” size=”3″/></td>
        <td>end: <input type=”text” id=”end” size=”3″/></td>
    </tr>
    <tr>
        <td colspan=”2″>
            <textarea id=”ta” onKeydown=”savePos(this)”
                              onKeyup=”savePos(this)”
                              onmousedown=”savePos(this)”
                              onmouseup=”savePos(this)”
                              onfocus=”savePos(this)”
                              rows=”14″ cols=”50″></textarea>
        </td>
    </tr>
    <tr>
        <td><input type=”text” id=”inputtext” /></td>
        <td><input type=”button” onClick=”add()” value=”Add Text”/></td>
    </tr>
</table>
</form>
</body>
</html>

附:IE 中的定义: http://msdn.microsoft.com/en-us/library/ms535872%28VS.85%29.aspx
http://msdn.microsoft.com/en-us/library/ms533042%28VS.85%29.aspx

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