<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 MoveCursortoPos(id,pos){//定位光标到某个位置
var obj = document.getElementById(id);
pos = pos ?pos :obj.value.length;
if (obj.createTextRange) {//IE浏览器
var range = obj.createTextRange();
range.moveStart("character", pos);
range.collapse(true);
range.select();
} else {//非IE浏览器
obj.setSelectionRange(obj.value.length, pos);
}
obj.focus();
}
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;
MoveCursortoPos("ta",start+document.getElementById("inputtext").value.length);
}
function savePos(textBox){
//如果是Firefox(1.5)的话，方法很简单
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。
// 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>
原文：http://my.oschina.net/122612475/blog/308375