<textarea id="content"></textarea>
<input type="text" id="input" value=""/>
<span id="add">增加字符</span>

$('#add').click(function(){
$('#content').insertAtCaret("这个是插入的文字开头,"+$('#input').val()+"这个是插入的文字结尾\n");
});

// 鼠标位置 插入 文字
jQuery.fn.extend({
insertAtCaret: function(myValue){
return this.each(function(i) {
if (document.selection) {
// for browsers like Internet Explorer
this.focus();
var sel = document.selection.createRange();
sel.text = myValue;
this.focus();
}
else if (this.selectionStart || this.selectionStart == '0') {
// for browsers like Firefox and Webkit based
var startPos = this.selectionStart;
var endPos = this.selectionEnd;
var scrollTop = this.scrollTop;
this.value = this.value.substring(0, startPos)+myValue+this.value.substring(endPos,this.value.length);
this.focus();
this.selectionStart = startPos + myValue.length;
this.selectionEnd = startPos + myValue.length;
this.scrollTop = scrollTop;
} else {
this.value += myValue;
this.focus();
}
});
}
});